Question

Which of the following statements about the cardiac cycle is CORRECT?

• A. At no time during the cardiac cycle are the mitral and aortic valves both open.
• B. The pressure in the left atrium exceeds that of the left ventricle throughout the ventricular ejection period.
• C. Most filling of the ventricle in diastole in a resting individual occurs with atrial contraction.
• D. The second heart sound is most closely associated with the closure of the left atrioventricular (mitral) valve.

Answer 1

Answer: (A)

Cardiac cycle has three stages: $1)$ Joint diastole: In this all the four chambers are relaxed and thus AV valves are open while semilunar are closed. $2)$ Atrial systole: Atria contract and AV valves are open. $3)$ Ventricular systole: Ventricles contract and thus semilunar valves open and AV close. Thus never both AV and semilunar are open. The pressure in left atrium exceeds that of left ventricle throughout the ventricle ejection period. First heart sound is LUB due to closure of AV valves and second heart sound is DUB due to closure of semilunar valves.