Mitral regurgitation in atrial fibrillation as heard at the apex

Electrocardiogram and phonocardiogram of mitral regurgitation as heard at the apex. After first heart sound (S1; closure of mitral and tricuspid valves), there is a harsh, holosystolic murmur of mitral regurgitation. Following second heart sound (S2; closure of the aortic and pulmonic valves), there is a third heart sound (S3), which results from rapid filling of a dilated left ventricle. An early diastolic murmur is due to the large volume of blood flow from the left atrium into the left ventricle, a result of mitral regurgitation.