22 Heart Anatomy & Conduction Practice Questions & Answers

1. 1. Oxygenated blood returns from the lungs to the heart. Which sequence does it follow from that point until it reaches the systemic circulation?

   • A.Left atrium → aortic valve → left ventricle → mitral valve → ascending aorta
   • B.Left atrium → mitral valve → left ventricle → pulmonic valve → pulmonary artery
   • C.Left atrium → tricuspid valve → left ventricle → pulmonic valve → aorta
   • D.Left atrium → mitral valve → left ventricle → aortic valve → aorta✓ Answer

   Blood leaving the lungs enters the left atrium, crosses the atrioventricular (mitral) valve into the left ventricle, and is ejected through the semilunar (aortic) valve into the aorta. Each side of the heart has the same architecture: an AV valve guards filling and a semilunar valve guards ejection, so the AV valve always comes before the semilunar valve. The tricuspid and pulmonic valves belong to the right side and never appear in the left-sided path.

   Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — chambers, valves and blood-flow sequenceReport a problem with this question

2. 2. A student says that every artery carries oxygenated blood and every vein carries deoxygenated blood. Which statement correctly describes the pulmonary vessels?

   • A.The pulmonary arteries carry oxygenated blood to the lungs and the pulmonary veins carry deoxygenated blood to the right atrium.
   • B.The pulmonary arteries carry deoxygenated blood to the lungs and the pulmonary veins return that same blood to the right atrium.
   • C.The pulmonary arteries carry deoxygenated blood to the lungs and the pulmonary veins carry oxygenated blood to the left atrium.✓ Answer
   • D.The pulmonary arteries carry oxygenated blood away from the lungs and the pulmonary veins deliver it to the left ventricle.

   Arteries and veins are defined by direction of flow, not by oxygen content: arteries carry blood away from the heart and veins carry blood toward it. In the pulmonary circuit the right ventricle sends deoxygenated blood out through the pulmonary arteries to the lungs, and the reoxygenated blood returns through the pulmonary veins into the left atrium. These are the two standard exceptions to the oxygen rule.

   Source: NHA CET Test Plan, Core Knowledge: anatomy and physiology of the cardiovascular system — pulmonary versus systemic circulationReport a problem with this question

3. 3. Why is the myocardium of the left ventricle thicker than the muscle of the other three chambers?

   • A.It must eject blood against the much higher resistance of the systemic circulation.✓ Answer
   • B.It holds a far larger volume of blood than any of the other three chambers.
   • C.It contracts before the other chambers and therefore carries the whole workload.
   • D.It must eject blood against the high resistance of the pulmonary circulation.

   Wall thickness reflects the pressure a chamber must generate, not the volume it holds. The left ventricle pumps into the aorta against systemic vascular resistance, which is several times higher than pulmonary resistance, so its myocardium is the thickest in the heart. The two ventricles eject roughly the same stroke volume and contract together, so neither volume nor timing explains the difference.

   Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — chamber structure and systemic versus pulmonary pressuresReport a problem with this question

4. 4. List the layers of the heart wall in order, starting with the layer that lines the chambers and touches the blood.

   • A.Epicardium, then myocardium, then endocardium
   • B.Endocardium, then myocardium, then epicardium✓ Answer
   • C.Myocardium, then endocardium, then epicardium
   • D.Endocardium, then epicardium, then myocardium

   The prefixes name the position: endo- means inner, myo- means muscle, epi- means upon or outer, so the wall runs endocardium, myocardium, epicardium from the blood outward. The endocardium is continuous with the endothelium of the great vessels, the myocardium is the contracting layer damaged in an infarction, and the epicardium is also the visceral layer of the pericardium. Reversing endocardium and epicardium is one of the most common errors on this topic.

   Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — layers of the heart wall and pericardiumReport a problem with this question

5. 5. Place the normal conduction pathway in order, beginning with the structure that normally starts the impulse.

   • A.SA node → AV node → Purkinje fibers → bundle of His → bundle branches → internodal pathways
   • B.SA node → internodal pathways → bundle of His → AV node → Purkinje fibers → bundle branches
   • C.SA node → internodal pathways → AV node → bundle of His → bundle branches → Purkinje fibers✓ Answer
   • D.AV node → internodal pathways → SA node → bundle of His → bundle branches → Purkinje fibers

   The impulse starts in the SA node, crosses the atria through the internodal pathways (with Bachmann's bundle carrying it to the left atrium) and produces the P wave, then reaches the AV node, where it is delayed. From the AV node it passes through the bundle of His, splits into the right and left bundle branches along the interventricular septum, and finally reaches the Purkinje fibers, which depolarize the ventricular muscle almost simultaneously and produce a narrow QRS.

   Source: NHA CET Test Plan: electrical conduction — normal conduction sequenceReport a problem with this question

6. 6. A fibrous skeleton separates the atria from the ventricles and does not conduct electricity. Which structure normally carries the impulse across that barrier?

   • A.The coronary sinus, which channels the impulse along the floor of the right atrium.
   • B.Bachmann's bundle, which carries the impulse from the right atrium to the left atrium.
   • C.The Purkinje network, which spreads the impulse straight from the atria to the ventricles.
   • D.The bundle of His, the only normal electrical link between atria and ventricles, via the AV node.✓ Answer

   The fibrous cardiac skeleton electrically insulates atrial muscle from ventricular muscle, so the only normal route across is the AV node into the bundle of His. That single gateway is what allows the AV node to delay every impulse and to block very rapid atrial rates from reaching the ventricles one for one. Bachmann's bundle stays within the atria, the Purkinje fibers lie below the bundle branches, and the coronary sinus is a vein rather than a conduction pathway.

   Source: NHA CET Test Plan: electrical conduction — AV junction and cardiac fibrous skeletonReport a problem with this question

7. 7. The AV node holds the impulse briefly before passing it to the ventricles. What does that delay accomplish?

   • A.The ventricles finish repolarizing so the T wave is complete before the next sinus impulse arrives.
   • B.The atria finish emptying into the ventricles, adding the final portion of ventricular filling.✓ Answer
   • C.The SA node has time to recharge fully so that it can fire again at its own intrinsic rate.
   • D.The coronary arteries fill during systole while the ventricular muscle is contracting hard.

   Most ventricular filling is passive, but the last portion depends on atrial contraction, the so-called atrial kick. The AV node delay gives the atria time to contract and empty before the ventricles begin to contract, which maximizes stroke volume. This is why losing organized atrial contraction, as in atrial fibrillation, reduces cardiac output even when the ventricular rate is controlled.

   Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — cardiac cycle, atrial contribution to ventricular fillingReport a problem with this question

8. 8. The SA node stops firing and the AV junction takes over as the pacemaker. What intrinsic rate should the technician expect from that site?

   • A.60 to 100 beats per minute
   • B.20 to 40 beats per minute
   • C.40 to 60 beats per minute✓ Answer
   • D.100 to 150 beats per minute

   Each pacemaker site has its own intrinsic firing rate: SA node 60 to 100, ectopic atrial foci 60 to 80, AV junction 40 to 60, and the ventricular Purkinje system 20 to 40 beats per minute. When the SA node fails, the AV junction becomes the next fastest backup and produces a junctional escape rhythm in the 40 to 60 range, usually with a narrow QRS because the impulse still uses the His-Purkinje system.

   Source: NHA CET Test Plan: heart anatomy and physiology — intrinsic pacemaker ratesReport a problem with this question

9. 9. A site in the ventricular Purkinje network is pacing the heart because every site above it has failed. What rate and QRS width follow from that origin?

   • A.40 to 60 beats per minute with a QRS wider than 0.12 sec
   • B.20 to 40 beats per minute with a QRS narrower than 0.12 sec
   • C.60 to 100 beats per minute with a QRS narrower than 0.12 sec
   • D.20 to 40 beats per minute with a QRS wider than 0.12 sec✓ Answer

   A ventricular pacemaker fires at its own slow intrinsic rate of 20 to 40 beats per minute, the lowest level of the pacemaker hierarchy. Because the impulse starts below the bundle branches, it spreads cell to cell through ventricular muscle instead of travelling down the fast His-Purkinje highway, so depolarization takes longer and the QRS widens beyond 0.12 sec. Rate and QRS width together point to where in the conduction system the beat began.

   Source: NHA CET Test Plan, electrical conduction, QRS duration and escape pacemaker ratesReport a problem with this question

10. 10. Several sites in the conduction system can generate impulses on their own. Which principle decides which site actually sets the heart's rhythm?

    • A.The site closest to the ventricular muscle fires first because the impulse travels less distance.
    • B.The site with the fastest intrinsic rate fires first and suppresses the slower sites below it.✓ Answer
    • C.The sites fire in turn, one beat each, so the rhythm is shared among all of them.
    • D.The site surrounded by the most muscle mass fires first and imposes its rhythm on the others.

    Whichever pacemaker reaches threshold first depolarizes the rest of the conduction system before the slower sites can finish charging, a mechanism called overdrive suppression. Because the SA node has the fastest intrinsic rate, it normally controls the heart and the lower sites remain silent backups. When the SA node slows or stops, the next fastest site escapes and takes over, which is why escape rhythms are protective rather than primary.

    Source: NHA CET Test Plan: heart anatomy and physiology — pacemaker hierarchy and escape mechanismsReport a problem with this question

11. 11. Atrial repolarization occurs during every cardiac cycle. Where does it appear on a normal EKG tracing?

    • A.It is recorded inside the QRS complex, hidden by the larger ventricular deflection.✓ Answer
    • B.It is recorded as the T wave that follows each QRS complex on the tracing.
    • C.It is recorded as the flat ST segment that lies between the QRS complex and the T wave.
    • D.It is recorded as the U wave that sometimes follows the T wave on the tracing.

    The size of a deflection depends on how much muscle mass is depolarizing or repolarizing. Atrial muscle is thin, so the atrial repolarization wave is small, and it happens at the same moment the far larger ventricular mass is depolarizing, so it is buried inside the QRS complex and cannot be seen separately. The T wave represents ventricular repolarization only.

    Source: NHA CET Test Plan: measuring EKG waveforms — waveform-to-event correspondenceReport a problem with this question

12. 12. The PR interval is measured from the start of the P wave to the start of the QRS complex. What does that span of time represent?

    • A.Atrial depolarization plus the delay at the AV node, up to the start of ventricular depolarization.✓ Answer
    • B.Ventricular depolarization plus the delay at the AV node, up to the start of atrial filling.
    • C.Atrial depolarization plus atrial contraction, up to the moment the atria begin to relax.
    • D.Atrial repolarization plus the delay at the AV node, up to the end of ventricular filling.

    The PR interval covers everything that happens from the moment the SA node impulse begins to spread through the atria until ventricular depolarization starts: atrial depolarization (the P wave) plus the conduction time through the AV node and bundle of His. The normal range is 0.12 to 0.20 sec, three to five small boxes at the standard 25 mm/sec paper speed. Because most of the interval is AV nodal conduction time, a lengthening PR interval points to delay at the AV node.

    Source: NHA CET Test Plan: measure EKG intervals and waveforms — PR interval 0.12-0.20 sec at 25 mm/secReport a problem with this question

13. 13. A technician measures the QT interval. What does this interval represent, and how does it behave when the heart rate rises?

    • A.Ventricular depolarization and repolarization together, and it lengthens as the heart rate rises.
    • B.Ventricular repolarization alone, and it stays fixed no matter how the heart rate changes.
    • C.Ventricular depolarization and repolarization together, and it shortens as the heart rate rises.✓ Answer
    • D.Atrial depolarization and repolarization together, and it shortens as the heart rate rises.

    The QT interval is measured from the beginning of the QRS complex to the end of the T wave, so it covers the whole period of ventricular electrical activity, both depolarization and recovery. Its duration varies inversely with heart rate: as the rate rises the cycle shortens and repolarization is completed more quickly, so the measured QT gets shorter. That is why raw QT values must always be read against the rate at which they were recorded.

    Source: NHA CET Test Plan: measure EKG intervals and waveforms — QT interval and its rate dependenceReport a problem with this question

14. 14. Why is a premature ventricular impulse that lands on the downslope of the T wave dangerous?

    • A.Cells are fully recovered, so the beat conducts normally and produces a narrow QRS complex.
    • B.Cells are partly recovered, so a strong stimulus can trigger a chaotic ventricular rhythm.✓ Answer
    • C.Cells cannot respond at all, so the impulse dies out and the ventricles produce no contraction.
    • D.Cells are still contracting, so the added beat tears the wall of the left ventricle.

    During the absolute refractory period, roughly the QRS through the peak of the T wave, the cells cannot respond to any stimulus. On the downslope of the T wave the heart is in the relative refractory or vulnerable period, where some cells have recovered and others have not, so a strong stimulus can capture part of the myocardium while the rest is still refractory. That uneven recovery sets up reentry, which is the R-on-T mechanism for ventricular tachycardia and ventricular fibrillation.

    Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — absolute and relative refractory periodsReport a problem with this question

15. 15. Which property of cardiac cells lets a site in the AV junction start firing on its own when the SA node fails?

    • A.Excitability, the ability to respond to an impulse that arrives from somewhere else.
    • B.Automaticity, the ability to depolarize spontaneously to threshold without any outside stimulus.✓ Answer
    • C.Contractility, the ability to shorten and pump blood when an impulse arrives.
    • D.Conductivity, the ability to pass an impulse from one cell on to the next one.

    Cardiac cells have four properties: automaticity, excitability, conductivity and contractility. Automaticity is the ability of pacemaker cells to depolarize spontaneously to threshold without any outside stimulus, and it is present in the SA node, the atrial foci, the AV junction and the ventricular Purkinje system. That is why a lower site can escape and pace the heart when the site above it fails.

    Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — properties of cardiac cellsReport a problem with this question

16. 16. A monitored patient shows organized narrow complexes at 70 per minute, but no carotid pulse can be felt. What does this situation reveal about the EKG?

    • A.The EKG records electrical activity only, so organized complexes can appear with no mechanical pumping at all.✓ Answer
    • B.The EKG records both events together, so an organized complex always proves a pulse is present.
    • C.The EKG records mechanical pumping, so the missing pulse means the electrodes are loose.
    • D.The EKG records electrical activity only, so the pulse must instead be checked at the femoral site.

    Depolarization is an electrical event that normally triggers, but does not guarantee, mechanical contraction, and the EKG records only the electrical half of that pair. Organized complexes with no pulse describe pulseless electrical activity, in which the conduction system is still working but the myocardium is not generating effective output. The rule for the technician is to assess the patient rather than the monitor and to get licensed help immediately.

    Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — electrical activity precedes and does not guarantee mechanical contractionReport a problem with this question

17. 17. A QRS complex measures 0.14 sec. What does that width tell the technician about the path the impulse took through the ventricles?

    • A.It started in the SA node and was held up inside the AV node before reaching the ventricles.
    • B.It crossed the fibrous skeleton straight from the atria without entering the septum.
    • C.It spread quickly along the His-Purkinje network from a site located above the AV node.
    • D.It spread slowly through muscle instead of using the fast His-Purkinje conduction network.✓ Answer

    QRS duration measures how long the ventricles take to depolarize, and the His-Purkinje network exists to make that happen almost simultaneously, which keeps the complex narrow. When the impulse originates in the ventricles or one bundle branch is blocked, part of the myocardium is activated cell to cell instead, which takes longer and widens the QRS to 0.12 sec or more. A wide QRS therefore means the normal high-speed pathway was not fully used.

    Source: NHA CET Test Plan: electrical conduction and QRS durationReport a problem with this question

18. 18. An inferior wall infarction often comes with bradycardia and AV block. Which anatomical fact explains that pairing, and which leads look at that wall?

    • A.The right coronary artery supplies the AV node in most people; leads II, III and aVF view it.✓ Answer
    • B.The left anterior descending artery supplies the AV node in most people; leads V1 to V4 view it.
    • C.The left circumflex artery supplies the AV node in most people; leads I, aVL, V5 and V6 view it.
    • D.The right coronary artery supplies the AV node in most people; leads V1 to V4 view that wall.

    The right coronary artery supplies the inferior wall of the left ventricle and, in roughly nine of ten people, the AV node as well, so the same blockage that injures the inferior wall also starves the AV node and produces bradycardia or AV block. The inferior wall is viewed by the contiguous leads II, III and aVF. The left anterior descending artery feeds the anterior and septal walls seen in V1 to V4, and the circumflex feeds the lateral wall seen in I, aVL, V5 and V6.

    Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — coronary circulation and lead-to-wall correspondenceReport a problem with this question

19. 19. Where in the heart is the SA node located?

    • A.In the upper wall of the right atrium, near the entrance of the superior vena cava.✓ Answer
    • B.In the upper wall of the left atrium, near the entrance of the pulmonary veins.
    • C.In the upper part of the interventricular septum, just below the aortic valve ring.
    • D.In the lower part of the interatrial septum, near the opening of the coronary sinus.

    The SA node sits high in the posterior wall of the right atrium where the superior vena cava enters, which is why the normal impulse spreads from upper right to lower left across the atria. That direction of travel moves toward the positive electrode of lead II, which is why a sinus P wave is upright in lead II. The AV node, by contrast, lies low in the interatrial septum near the coronary sinus opening.

    Source: NHA CET Test Plan: electrical conduction — location of the sinoatrial nodeReport a problem with this question

20. 20. A patient's heart rate climbs to 170 per minute. Why does blood flow through the coronary arteries fall at that rate?

    • A.The coronary arteries fill during systole, and systole shortens steadily as the rate climbs.
    • B.The coronary arteries fill during diastole, and diastole shortens as the rate climbs.✓ Answer
    • C.The coronary arteries branch off the aorta below the valve and close at fast rates.
    • D.The coronary arteries fill only while the ventricles contract, and that contraction weakens.

    The coronary arteries arise from the ascending aorta just above the aortic valve, and the myocardium perfuses mainly during diastole, when the relaxed ventricular muscle is no longer squeezing its own vessels shut. As heart rate rises, diastole shortens far more than systole does, so the window for coronary filling narrows just as the muscle's oxygen demand is highest. That mismatch is why sustained tachycardia can produce ischemia.

    Source: NHA CET Test Plan, Core Knowledge: basic anatomy and physiology of the heart — coronary perfusion during diastoleReport a problem with this question

21. 21. What decides whether a wave appears as an upright deflection or an inverted one in a particular lead?

    • A.Whether the electrode was placed on a limb or on the chest wall over the precordium.
    • B.Whether the tissue that is depolarizing at that moment is atrial muscle or ventricular muscle.
    • C.Whether the chamber being depolarized sits on the right or on the left side of the heart.
    • D.Whether the wave of depolarization travels toward or away from that lead's positive electrode.✓ Answer

    Every lead is a viewing axis with a positive and a negative electrode, and the machine writes an upward deflection whenever the wave of depolarization moves toward the positive electrode and a downward one when it moves away. Because normal sinus depolarization travels from the upper right atrium toward the lower left, the P wave and QRS are normally upright in lead II. The same rule explains why deflections are largely negative in aVR on a correctly applied tracing.

    Source: NHA CET Test Plan: lead axes and direction of depolarizationReport a problem with this question

22. 22. The apex of the left ventricle points downward and to the left. Which chest electrode sits over that landmark?

    • A.V2, at the fourth intercostal space at the left sternal border.
    • B.V1, at the fourth intercostal space at the right sternal border.
    • C.V4, at the fifth intercostal space in the left midclavicular line.✓ Answer
    • D.V6, at the fifth intercostal space in the left midaxillary line.

    The heart lies obliquely in the mediastinum with its apex directed down and to the left, which places the apex at the fifth intercostal space in the midclavicular line, the same spot where the apical pulse is palpated. V4 is positioned there by anatomical landmark, and V5 and V6 are then placed level with V4 along the anterior axillary and midaxillary lines. V3 is placed after V4 because it must fall midway between V2 and V4.

    Source: NHA CET Test Plan: apply electrodes and attach leads — precordial electrode landmarksReport a problem with this question

Practice questions based on the NHA Certified EKG Technician (CET) test plan, the standard 12-lead electrode positions defined by anatomical landmark, and durable cardiac electrophysiology. CET is a mark of the National Healthcareer Association; this site is not affiliated with or endorsed by NHA. An EKG technician records tracings and does not diagnose. Always follow your facility's policies, your state's scope of practice, and the direction of the ordering provider. About the CET exam →