Which valves close during the 1st heart sound?

The first heart sound, often referred to as "S1," is primarily associated with the closure of the mitral and tricuspid valves. During this phase of the cardiac cycle, the ventricles contract, and the pressure within them rises. This increase in pressure causes the mitral valve, which separates the left atrium from the left ventricle, and the tricuspid valve, which separates the right atrium from the right ventricle, to close. The closure of these valves prevents the backflow of blood into the atria as the ventricles eject blood into the aorta and pulmonary artery.

In contrast, the pulmonary and aortic valves, which are responsible for blood flow out of the heart to the lungs and the rest of the body, respectively, close during the second heart sound (S2). Therefore, focusing on the timing and the role of each valve is crucial to understanding the events that correlate with the sounds produced during the cardiac cycle. The correct answer emphasizes the importance of the mitral and tricuspid valves' closure in relation to the first heart sound.