Cardiac Cycle and Hemodynamics Practice Questions
21 free Cardiac Cycle and Hemodynamics practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following best describes the first sound (S1) heard during the cardiac cycle?
- A Closure of the aortic and pulmonary valves
- B Closure of the mitral and tricuspid valves
- C Opening of the semilunar valves
- D Onset of isovolumetric relaxation
Correct answer: Closure of the mitral and tricuspid valves
S1 (“lub”) is produced by closure of the atrioventricular valves (mitral and tricuspid) at the beginning of ventricular systole when pressure in ventricles rises. This marks the end of ventricular filling and start of isovolumetric contraction.
During which phase of the cardiac cycle does isovolumetric contraction occur?
- A After atrial systole, before semilunar valves open
- B During rapid ejection of blood into the aorta
- C During isovolumetric relaxation of the ventricle
- D During passive ventricular filling phase
Correct answer: After atrial systole, before semilunar valves open
Isovolumetric contraction begins right after atrioventricular valve closure (after atrial systole) and before the semilunar valves open. The ventricles contract, pressure rises, but volume remains constant because all valves are closed.
How is stroke volume (SV) defined in terms of ventricular volumes?
- A SV = End-diastolic volume (EDV) + end-systolic volume (ESV)
- B SV = ESV – EDV
- C SV = EDV – ESV
- D SV = EDV / ESV
Correct answer: SV = EDV – ESV
Stroke volume is the amount of blood ejected per beat and equals end-diastolic volume minus end-systolic volume (SV = EDV – ESV).
Which factor does NOT increase stroke volume under physiologic conditions?
- A Increased preload
- B Increased contractility
- C Decreased afterload
- D Increased afterload
Correct answer: Increased afterload
Stroke volume increases with increased preload or contractility and decreases with increased afterload, because higher afterload means the ventricle must work against greater resistance, reducing ejection.
What does preload most directly reflect in the context of cardiac function?
- A Arterial pressure the ventricle must overcome to eject blood
- B Ventricular end-diastolic volume and fiber stretch before contraction
- C Contractile strength of myocytes independent of fiber length
- D Ventricular end-systolic volume after contraction
Correct answer: Ventricular end-diastolic volume and fiber stretch before contraction
Preload refers to the degree of stretch of myocardial fibers at end-diastole, which is proportional to the end-diastolic volume (or pressure) — determining how much the ventricle is filled before contraction.
Which of the following defines afterload for the left ventricle in most physiologic descriptions?
- A End-diastolic filling volume of the left ventricle
- B Arterial pressure and resistance opposing ejection
- C Intrinsic contractility of the cardiac muscle fibers
- D Venous return of blood into the heart
Correct answer: Arterial pressure and resistance opposing ejection
Afterload represents the resistance the ventricle must overcome to eject blood, primarily determined by arterial pressure and vascular resistance during systole.
Which equation correctly defines cardiac output (CO)?
- A CO = SV × ESV
- B CO = EDV – ESV
- C CO = SV × HR
- D CO = HR ÷ SV
Correct answer: CO = SV × HR
Cardiac output equals stroke volume (SV) multiplied by heart rate (HR), representing the volume of blood pumped per minute by the ventricle.
According to the Frank–Starling mechanism, what happens when venous return to the heart increases acutely (within the physiologic range)?
- A Stroke volume decreases due to increased afterload
- B Stroke volume rises as greater preload stretches fibers
- C Heart rate decreases regardless of preload changes
- D Contractility becomes independent of fiber length
Correct answer: Stroke volume rises as greater preload stretches fibers
As venous return increases, end-diastolic volume rises, stretching myocardial fibers and increasing preload, which enhances ventricular contractile force and increases stroke volume — per the Frank–Starling mechanism.
Which phase of the cardiac cycle corresponds to the rapid ejection phase when aortic valve opens and blood is expelled into the aorta?
- A Isovolumetric relaxation
- B Ventricular filling
- C Isovolumetric contraction
- D Ventricular ejection (systole)
Correct answer: Ventricular ejection (systole)
After ventricular pressure exceeds aortic pressure, the aortic valve opens and the ventricle ejects blood — the ventricular ejection phase of systole.
What effect does an acute increase in systemic vascular resistance (i.e., increased afterload) have on stroke volume if other factors remain constant?
- A Stroke volume increases
- B Stroke volume remains unchanged
- C Stroke volume decreases
- D Stroke volume becomes equal to end-diastolic volume
Correct answer: Stroke volume decreases
An acute increase in afterload makes it harder for the ventricle to eject blood. If preload and contractility remain constant, stroke volume will decrease.
During which part of the cardiac cycle does isovolumetric relaxation occur?
- A Immediately after atrial systole ends
- B After aortic valve closes, before mitral opens
- C During rapid ventricular ejection of blood
- D During atrial contraction phase
Correct answer: After aortic valve closes, before mitral opens
Isovolumetric relaxation follows aortic valve closure and precedes opening of the mitral valve; ventricles relax, pressure falls, but volume remains constant because all valves are closed.
Which of the following best reflects the relationship between end-diastolic volume (EDV) and myocardial fiber stretch regarding preload?
- A Higher EDV leads to decreased myocardial fiber stretch
- B Preload is unrelated to EDV
- C Higher EDV leads to increased myocardial fiber stretch
- D Preload refers to post-systolic myocardial tension
Correct answer: Higher EDV leads to increased myocardial fiber stretch
Preload is proportional to EDV because a larger EDV stretches myocardial fibers more at end-diastole, increasing sarcomere length and preload.
What is the primary determinant of the afterload faced by the left ventricle under physiologic conditions?
- A Left ventricular end-diastolic filling volume
- B Pulmonary venous filling pressure
- C Systemic arterial pressure and vascular resistance
- D Right atrial filling pressure
Correct answer: Systemic arterial pressure and vascular resistance
Afterload is largely determined by the pressure the left ventricle must overcome to eject blood — essentially systemic arterial pressure and systemic vascular resistance.
Which of the following statements about cardiac output (CO) is correct under steady-state physiology?
- A CO of the left ventricle is always double that of the right ventricle
- B CO equals venous return
- C CO is independent of venous return
- D CO equals EDV minus ESV
Correct answer: CO equals venous return
In steady state, cardiac output must equal venous return, because whatever volume is returned to the heart must be pumped out.
If sympathetic stimulation increases heart contractility (inotropy) without changing preload or afterload, what happens to stroke volume and ejection fraction (EF)?
- A Stroke volume increases, EF increases
- B Stroke volume increases, EF decreases
- C Stroke volume decreases, EF increases
- D No change in stroke volume or EF
Correct answer: Stroke volume increases, EF increases
Increased contractility enhances ventricular ejection, raising stroke volume. Since EDV remains similar, a higher SV means a higher ejection fraction.
Which event in the cardiac cycle corresponds most closely with the peak of the QRS complex on ECG in the context of mechanical events?
- A Onset of atrial contraction
- B Closure of semilunar valves
- C Isovolumetric contraction
- D Isovolumetric relaxation
Correct answer: Isovolumetric contraction
The QRS complex represents ventricular depolarization, which triggers ventricular contraction. Mechanically, this corresponds to isovolumetric contraction phase, as ventricles generate pressure with all valves closed.
Which change would you expect in the left ventricular pressure–volume loop if afterload is acutely increased (e.g., acute hypertension)?
- A Leftward shift in the loop with increased stroke volume
- B Rightward shift, higher end-diastolic volume, lower stroke volume
- C A taller but narrower loop reflecting increased contractility
- D No change in end-diastolic or end-systolic volumes
Correct answer: Rightward shift, higher end-diastolic volume, lower stroke volume
An acute afterload increase means the ventricle must generate higher pressure before ejection; this delays ejection, leading to increased end-diastolic volume (preload), and typically reduces stroke volume — shifting the loop rightward.
Which of the following reflexes increases heart rate in response to increased venous return/stretch of the right atrium?
- A Baroreceptor reflex
- B Bainbridge reflex
- C Frank–Starling reflex
- D Meyer–Fenster reflex
Correct answer: Bainbridge reflex
The Bainbridge reflex increases heart rate when rising venous return stretches the right atrium, thereby matching cardiac output to the increased blood volume.
Which phase of the cardiac cycle contributes most to ventricular filling at rest under normal physiology?
- A Atrial systole (atrial kick)
- B Isovolumetric contraction
- C Early diastolic rapid filling
- D Isovolumetric relaxation
Correct answer: Early diastolic rapid filling
During early diastole, after semilunar valve closure and mitral valve opening, rapid passive ventricular filling delivers the majority of ventricular volume. Atrial systole contributes a smaller proportion at rest.
Which of the following best explains why an increased heart rate alone may not substantially increase cardiac output under certain conditions?
- A Because reduced filling time lowers stroke volume
- B Because preload automatically increases with HR
- C Because afterload decreases at high heart rates
- D Because contractility falls with increased HR
Correct answer: Because reduced filling time lowers stroke volume
With a very high heart rate, diastole shortens and there is less time for ventricular filling, reducing preload and stroke volume, which may offset the gain in output from increased beats per minute.
What happens to ejection fraction (EF) if end-systolic volume (ESV) increases but end-diastolic volume (EDV) remains constant?
- A EF increases
- B EF decreases
- C EF remains unchanged
- D EF becomes greater than 100%
Correct answer: EF decreases
Ejection fraction is defined as SV/EDV, i.e., (EDV – ESV)/EDV. If ESV increases while EDV is unchanged, SV decreases, so EF decreases.