Mitral valve prolapse as heard with the patient squatting

Electrocardiogram and phonocardiogram of mitral valve prolapse as heard at the apex. S₁ (mitral and tricuspid valve closure) is followed by a midsystolic click resulting from the prolapsing mitral valve, after which there is a systolic murmur of mitral regurgitation. With squatting, there is an increase in systemic vascular resistance or afterload and an increase in left ventricular pressure and volume. As a result, there is a delay in mitral valve closure and the prolapse (and click) are delayed, occurring late in systole. Consequently, the mitral regurgitation murmur is late and shortened.