"Presystolic" augmentation of diastolic heart sounds in atrial fibrillation

In the presence of atrial fibrillation, the diastolic murmur of mitral stenosis can appear augmented during early systole before the mitral valve closure sound. This phenomenon has previously been thought to be due to increased blood flow velocity across the narrowing mitral valve orifice. We have observed patients in whom the third heart sound (S3) gallop, the diastolic flow murmur of atrial septal defect and mitral insufficiency and the initial muscular component of the first heart sound become more intense during this period with short, critically timed cycle lengths. This phenomenon appears to be neither peculiar to nor indicative of mitral stenosis and is probably a direct result of the initial muscular contraction of an underfilled ventricle. Either the contraction itself or the sudden deceleration of the rapidly moving flow of blood across the atrioventricular orifice may produce the sound.