Which valves are closing during the first heart sound?

The first heart sound, often referred to as S1, is produced primarily by the closing of the mitral and tricuspid valves. This sound marks the onset of ventricular contraction (systole) and occurs just before the ventricles begin to pump blood into the arteries.

When the heart contracts, the pressure within the ventricles increases, leading to the closure of these atrioventricular valves (mitral and tricuspid) to prevent backflow of blood into the atria. The closure of these valves is crucial for ensuring that blood flows in a forward direction from the heart to the pulmonary artery and aorta.

While other valves, such as the aortic and pulmonary valves, do close during the cardiac cycle, their closure occurs later in the cycle, contributing to the second heart sound (S2). Understanding the mechanics of the heart sounds helps in diagnosing various cardiac conditions and appreciating the normal functioning of the heart.