Question 1

Which of the following best describes the function of the sinoatrial (SA) node in the heart's intrinsic conduction system?

Accepted Answer

It acts as the heart's natural pacemaker, initiating action potentials that set the heart rate.

Question 2

During the pacemaker potential in SA node cells, which ion's movement is primarily responsible for the gradual depolarization toward threshold?

Accepted Answer

Influx of cations (mainly $$\mathrm{Na^+}) $$through leakage channels

Question 3

Which event is represented by the QRS complex on an electrocardiogram (ECG)?

Accepted Answer

Ventricular depolarization

Question 4

A patient presents with a heart rate of 45 beats per minute and an ECG showing absent P waves. Which of the following is the most likely explanation?

Accepted Answer

The AV node has taken over as the pacemaker due to SA node failure.

Question 5

Which of the following best explains why tetanus (sustained contraction) cannot occur in cardiac muscle?

Accepted Answer

The absolute refractory period in cardiac muscle is very long, preventing summation of contractions.

Question 6

A patient is undergoing a stress test with ECG monitoring. What is the primary reason for performing an ECG during exercise rather than at rest?

Accepted Answer

Exercise increases the demand for oxygen, making it easier to detect blockages and abnormal heart rhythms.

Question 7

Which formula correctly calculates cardiac output ($$CO$$)?

Accepted Answer

$$CO = HR 	imes SV$$

Question 8

If a patient has an end diastolic volume ($$EDV) of 120 mL $$and an end systolic volume ($$ESV) of 50 mL$$, what is the stroke volume ($$SV$$)?

Accepted Answer

$$SV = EDV - ESV = 70\ \mathrm{mL}$$

Question 9

Which of the following would most likely increase stroke volume ($$SV$$)?

Accepted Answer

Increased preload due to greater venous return

Question 10

A patient with left-sided heart failure is most likely to develop which of the following complications?

Accepted Answer

Pulmonary edema

Question 11

Which of the following best describes the effect of sympathetic nervous system activation on the heart?

Accepted Answer

It increases heart rate and contractility by releasing norepinephrine.

Question 12

Which of the following is a likely cause of a heart murmur heard between the first and second heart sounds?

Accepted Answer

Stenosis or insufficiency of the atrioventricular (AV) valves

Question 13

Which of the following best explains the Frank-Starling Law of the Heart?

Accepted Answer

The greater the stretch of cardiac muscle fibers before contraction, the stronger the force of contraction.

Question 14

Which of the following best describes the plateau phase of the cardiac contractile cell action potential?

Accepted Answer

It is maintained by the influx of $$\mathrm{Ca$$^{2+}$$}$$ ions through slow calcium channels.

Question 15

A second-degree heart block is characterized by which of the following ECG findings?

Accepted Answer

Some P waves not followed by QRS complexes, resulting in more P waves than QRS complexes

Question 16

Which of the following would be considered a positive inotropic agent?

Accepted Answer

Norepinephrine

Question 17

During which phase of the cardiac cycle are all four heart valves closed and the ventricles are contracting but not yet ejecting blood?

Accepted Answer

Isovolumetric contraction

Question 18

Which of the following best explains why the action potential duration in cardiac muscle is much longer than in skeletal muscle?

Accepted Answer

The plateau phase due to slow $$\mathrm{Ca$$^{2+}$$}$$ influx prolongs depolarization.

Question 19

A patient with a heart rate of 120 beats per minute is said to have which of the following?

Accepted Answer

Tachycardia

Question 20

Which of the following is the correct sequence of electrical conduction through the heart?

Accepted Answer

SA node → AV node → Bundle branches → Purkinje fibers

The Heart – Electrical Activity, Pacemaker Cells, and the Cardiac Cycle

Study Guide - Practice Questions