Note that during systole the aortic valve is open, allowing ejection of blood from the left ventricle into the aorta. The mitral valve is closed, preventing blood from regurgitating back into the left atrium. In contrast, during diastole the aortic valve is closed, preventing regurgitation of blood from the aorta back into the left ventricle. The mitral valve is open, allowing blood to flow from the left atrium into the relaxed left ventricle.
Understanding the interrelationships of the pressures in these three chambers—left atrium, left ventricle, and aorta—together with the position and movement of the valves is fundamental to understanding heart sounds. These changing pressures and the sounds that result are traced here through one cardiac cycle. Note that during auscultation the first and second heart sounds define the duration of systole and diastole.
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