Q: If a patient has an end diastolic volume (EDV) of 130 mL and an end systolic volume (ESV) of 60 mL, what is the stroke volume (SV)?

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

Question 1

Which of the following best describes the sequence of events in the intrinsic cardiac conduction system, starting from the pacemaker?

Accepted Answer

Sinoatrial node → Atrioventricular node → AV bundle → Bundle branches → Purkinje fibers

Question 2

During the pacemaker potential phase in cardiac pacemaker cells, which ion channels are primarily responsible for the slow depolarization?

Accepted Answer

Slow Na$$^+$$ channels and closing of K$$^+$$ channels

Question 3

What is the main effect of the plateau phase in the action potential of contractile cardiac muscle cells?

Accepted Answer

It prevents tetanic contractions by prolonging depolarization

Question 4

A patient’s ECG shows absent P waves and a heart rate of 45 beats per minute. Which of the following is the most likely explanation?

Accepted Answer

The SA node is nonfunctional, and the AV node is pacing the heart (junctional rhythm)

Question 5

Which equation correctly represents cardiac output (CO)?

Accepted Answer

$$CO = HR 	imes SV$$

Question 6

If a patient has an end diastolic volume (EDV) of 130 mL and an end systolic volume (ESV) of 60 mL, what is the stroke volume (SV)?

Accepted Answer

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

Question 7

Which of the following would most likely increase the force of cardiac muscle contraction (contractility)?

Accepted Answer

Release of epinephrine from the adrenal medulla

Question 8

A patient with persistent high blood pressure has an aortic pressure of 100 mm Hg. What effect does this have on afterload and stroke volume?

Accepted Answer

Afterload increases, and stroke volume decreases

Question 9

Which of the following best explains why the heart cannot undergo tetanic contractions?

Accepted Answer

The refractory period in cardiac muscle is longer than the contraction itself

Question 10

Which of the following changes would most likely be seen in the ECG of a patient with ventricular fibrillation?

Accepted Answer

Chaotic, grossly abnormal ECG deflections

Question 11

A patient is experiencing a heart rate of 120 beats per minute at rest. Which term best describes this condition, and what is a potential consequence if it persists?

Accepted Answer

Tachycardia; may lead to fibrillation

Question 12

Which of the following best describes the effect of acetylcholine on the heart?

Accepted Answer

It decreases heart rate by opening K$$^+$$ channels in pacemaker cells

Question 13

Which phase of the cardiac cycle is characterized by all heart valves being closed and no change in ventricular volume?

Accepted Answer

Isovolumetric contraction

Question 14

A patient with a defective mitral valve that does not close completely is likely to experience which of the following?

Accepted Answer

A swishing sound due to blood regurgitating into the left atrium

Question 15

Which of the following is the most important factor in determining preload in the heart?

Accepted Answer

Venous return

Question 16

Which of the following best describes the Frank-Starling law of the heart?

Accepted Answer

The greater the preload (stretch), the greater the force of contraction

Question 17

Which of the following would most likely be seen in a patient with left-sided heart failure?

Accepted Answer

Pulmonary congestion

Question 18

Which of the following is a direct effect of sympathetic stimulation on the heart?

Accepted Answer

Increased heart rate and force of contraction

Question 19

A 25-year-old athlete has a resting heart rate of 55 beats per minute. Which of the following best explains this finding?

Accepted Answer

The athlete has bradycardia, which may be a desirable result of endurance training

Question 20

Which of the following congenital heart defects results in the mixing of oxygen-poor and oxygen-rich blood?

Accepted Answer

Patent ductus arteriosus

Electrical and Mechanical Events of the Heart: Cardiac Physiology and Regulation

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