The first heart sound S1 is associated with which events?

The first heart sound S1 is associated with which events?

• A. Beginning of systole; ventricle is depolarized; closure of the AV valves.
• B. Closure of the semilunar valves.
• C. Ventricular repolarization.
• D. Atrial contraction.

Answer: (A)

S1 marks the start of ventricular systole, produced when the atrioventricular valves (mitral and tricuspid) close as the ventricles begin to contract and pressure rises after ventricular depolarization. This event occurs around the time of the QRS complex on the ECG, signaling the transition from filling to pumping. The closing of these valves creates the characteristic “lub” of S1. The second heart sound comes from the closure of the semilunar valves later in systole, not from S1. Ventricular repolarization (the T wave) is an electrical event that occurs after S1, and atrial contraction happens during late diastole, not at the onset of systole.

S1 marks the start of ventricular systole, produced when the atrioventricular valves (mitral and tricuspid) close as the ventricles begin to contract and pressure rises after ventricular depolarization. This event occurs around the time of the QRS complex on the ECG, signaling the transition from filling to pumping. The closing of these valves creates the characteristic “lub” of S1. The second heart sound comes from the closure of the semilunar valves later in systole, not from S1. Ventricular repolarization (the T wave) is an electrical event that occurs after S1, and atrial contraction happens during late diastole, not at the onset of systole.