Cardiac Cycle and Heart Sounds Practice Questions
20 free Cardiac Cycle and Heart Sounds practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which phase of the cardiac cycle is characterized by all four heart valves being closed while ventricular pressure rises rapidly?
- A Isovolumetric contraction
- B Atrial systole
- C Ventricular ejection
- D Isovolumetric relaxation
Correct answer: Isovolumetric contraction
During isovolumetric contraction, the ventricles begin to contract, raising pressure enough to close the AV valves but not yet enough to open the semilunar valves. Because no blood enters or leaves the ventricles, the volume remains constant while pressure spikes.
The first heart sound (S1) is primarily caused by which of the following mechanical events?
- A Closure of the semilunar valves
- B Opening of the atrioventricular valves
- C Blood rushing into the aorta
- D Closure of the atrioventricular valves
Correct answer: Closure of the atrioventricular valves
S1 occurs at the beginning of ventricular systole. The sudden rise in ventricular pressure forces the mitral and tricuspid valves shut, creating vibrations in the valves and surrounding myocardium.
During which phase of the cardiac cycle does the aortic valve open?
- A Ventricular ejection
- B Isovolumetric contraction
- C Atrial systole
- D Isovolumetric relaxation
Correct answer: Ventricular ejection
The aortic valve opens when left ventricular pressure exceeds the pressure in the aorta. This marks the transition from isovolumetric contraction to the ventricular ejection phase.
The second heart sound (S2) marks the beginning of which phase?
- A Isovolumic relaxation
- B Ventricular systole
- C Ventricular filling
- D Atrial contraction
Correct answer: Isovolumic relaxation
S2 is caused by the closure of the semilunar valves (aortic and pulmonary) at the end of ventricular ejection. This event initiates the isovolumetric relaxation phase of diastole.
What occurs during the 'dicrotic notch' (incisura) seen on an aortic pressure curve?
- A A brief rise in pressure from aortic valve closure
- B A sudden drop in pressure as the mitral valve opens
- C The peak pressure reached during systole
- D The point of maximum ventricular filling
Correct answer: A brief rise in pressure from aortic valve closure
The dicrotic notch is a short-lived increase in aortic pressure following the closure of the aortic valve. It is caused by a slight backflow of blood against the closed valve leaflets and the elastic recoil of the aortic wall.
In a healthy adult at rest, what percentage of ventricular filling is typically attributed to atrial contraction (the 'atrial kick')?
- A 10-20%
- B 50-60%
- C 75-80%
- D 95-100%
Correct answer: 10-20%
At rest, the majority of ventricular filling occurs passively during early diastole. Atrial contraction only contributes a final 10-20% to the end-diastolic volume, though this becomes more critical at high heart rates.
The third heart sound (S3), if heard, occurs during which phase of the cardiac cycle?
- A Atrial systole
- B Isovolumetric contraction
- C Isovolumetric relaxation
- D Rapid ventricular filling
Correct answer: Rapid ventricular filling
S3 is a low-frequency sound heard early in diastole. It is caused by the vibration of the ventricular walls during the period of rapid, passive filling from the atria.
During isovolumetric relaxation, which of the following is true regarding ventricular volume?
- A It is increasing rapidly
- B It is decreasing slowly
- C It remains constant at the end-diastolic volume
- D It remains constant at the end-systolic volume
Correct answer: It remains constant at the end-systolic volume
In isovolumetric relaxation, all valves are closed, meaning no blood can enter the ventricle. The volume is at its lowest point in the cycle, known as the end-systolic volume (ESV).
A fourth heart sound (S4) is most commonly associated with which of the following?
- A Chronic aortic valve regurgitation
- B Non-compliant ventricle in atrial systole
- C Normal rapid ventricular filling in children
- D Sudden closure of the tricuspid valve
Correct answer: Non-compliant ventricle in atrial systole
S4 occurs late in diastole, coinciding with atrial systole. It is caused by the atria pushing blood into a ventricle that is resistant to filling, often due to hypertrophy or fibrosis.
The 'v' wave of the jugular venous pulse corresponds to which event in the cardiac cycle?
- A Atrial contraction during late diastole
- B Bulging of the tricuspid valve into the atrium
- C Venous filling against a closed tricuspid valve
- D Rapid emptying of the atrium into the ventricle
Correct answer: Venous filling against a closed tricuspid valve
The 'v' wave represents the rise in atrial pressure during ventricular systole as blood returns from the veins while the AV valves are still closed.
At which point in the cardiac cycle is ventricular volume at its maximum?
- A End of atrial systole phase
- B End of isovolumetric contraction
- C Beginning of atrial systole
- D End of ventricular ejection
Correct answer: End of atrial systole phase
Ventricular volume reaches its peak at the end of diastole, just after atrial contraction is complete. This volume is known as the End-Diastolic Volume (EDV).
Which of the following heart sounds is often referred to as an 'atrial gallop'?
- A S1
- B S2
- C S3
- D S4
Correct answer: S4
S4 is called an atrial gallop because it occurs during atrial contraction. S3 is known as a ventricular gallop because it occurs during the passive filling phase.
What is the primary factor that causes the AV valves to open?
- A Contraction of the papillary muscles
- B Atrial pressure exceeding ventricular pressure
- C Ventricular pressure exceeding aortic pressure
- D The P-wave of the EKG
Correct answer: Atrial pressure exceeding ventricular pressure
The AV valves are passive structures. They open simply when the pressure in the atria becomes higher than the pressure in the relaxing ventricles, allowing blood to flow down the pressure gradient.
During the 'reduced ejection' phase, why does blood continue to flow into the aorta even though ventricular pressure is slightly falling?
- A The atrium is pulling blood out of the ventricle
- B The kinetic energy (momentum) of the flowing blood
- C The aortic valve is being pulled open by the papillary muscles
- D The ventricles are expanding to create a vacuum
Correct answer: The kinetic energy (momentum) of the flowing blood
In late systole, the pressure gradient actually reverses slightly, but the momentum of the blood and the compliance of the great vessels allow outflow to continue until the semilunar valves finally close.
Which phase of the cardiac cycle has the longest duration at a resting heart rate?
- A Atrial systole
- B Isovolumetric contraction
- C Ventricular ejection
- D Ventricular filling
Correct answer: Ventricular filling
Diastole (filling) is normally significantly longer than systole. As heart rate increases, the duration of diastole shortens more dramatically than the duration of systole.
The 'a' wave of the atrial pressure curve is produced by:
- A Atrial depolarization
- B Contraction of the atria
- C Ventricular contraction
- D Closure of the AV valves
Correct answer: Contraction of the atria
The 'a' wave is the first peak in atrial pressure and is caused by the actual mechanical contraction of the atrial myocardium.
Physiological splitting of the second heart sound (S2) during inspiration is due to:
- A Earlier closure of the mitral valve
- B Delayed closure of the pulmonic valve
- C Delayed closure of the aortic valve
- D Earlier closure of the tricuspid valve
Correct answer: Delayed closure of the pulmonic valve
Inspiration lowers intrathoracic pressure, increasing venous return to the right heart. This increases the stroke volume of the right ventricle, taking longer to eject and thus delaying the closure of the pulmonic valve.
Which EKG event immediately precedes the isovolumetric contraction phase?
- A P wave
- B QRS complex
- C T wave
- D U wave
Correct answer: QRS complex
The QRS complex represents ventricular depolarization, which triggers the mechanical contraction of the ventricles that begins with the isovolumetric phase.
Stroke volume is mathematically defined as:
- A EDV + ESV
- B Heart Rate / Cardiac Output
- C ESV / EDV
- D EDV - ESV
Correct answer: EDV - ESV
Stroke volume is the amount of blood ejected in one beat. It is the difference between the volume of the ventricle at the end of filling (EDV) and the volume remaining after ejection (ESV).
During the 'diastasis' phase of the cardiac cycle:
- A The atria contract forcefully
- B The ventricles are ejecting blood at a slow rate
- C Passive ventricular filling slows significantly
- D All heart valves are closed and the heart is motionless
Correct answer: Passive ventricular filling slows significantly
Diastasis is the middle period of diastole between rapid filling and atrial contraction. During this phase, the pressures in the atria and ventricles are nearly equal, and filling occurs very slowly.