What is the first sound of the heart?

What is the first sound of the heart?

• A. Systolic sound, associated with isovolumetric ventricular contraction.
• B. Diastolic sound, associated with isovolumetric ventricular relaxation.
• C. Murmur due to valve disease.
• D. Noise from blood flow.

Answer: (A)

The first heart sound comes from the moment the ventricles begin to contract and the atrioventricular valves (the mitral and tricuspid valves) snap shut. This happens at the start of systole, during the isovolumetric contraction phase when the ventricles are building pressure with all valves closed. The closing of these valves creates a crisp “lub” sound, which is the first heart sound. It marks the beginning of systole, before the semilunar valves open to eject blood. The other options describe sounds that are either associated with the end of systole and start of diastole (the second heart sound from semilunar valve closure) or are abnormal/noise rather than the normal valve-closure sound.

The first heart sound comes from the moment the ventricles begin to contract and the atrioventricular valves (the mitral and tricuspid valves) snap shut. This happens at the start of systole, during the isovolumetric contraction phase when the ventricles are building pressure with all valves closed. The closing of these valves creates a crisp “lub” sound, which is the first heart sound. It marks the beginning of systole, before the semilunar valves open to eject blood. The other options describe sounds that are either associated with the end of systole and start of diastole (the second heart sound from semilunar valve closure) or are abnormal/noise rather than the normal valve-closure sound.