Presystolic murmur

A presystolic murmur, also called presystolic accentuation, is a type of diastolic heart murmur typically associated with the opening snap in mitral valve stenosis. It is heard following the middiastolic rumble of the stenotic valve,^[1] during the diastasis phase, making it a "late diastolic" murmur.

The murmur is heard due to antegrade flow of blood through a progressively narrowing mitral opening during the end of the atrial systole. This antegrade flow through the mitral valve before it completely closes appears to be the result of a pressure gradient at the end of diastole.^[1] As its name indicates, the presystolic murmur is heard before the mitral valve produces the S1 heart sound.

Less often, a presystolic murmur can be heard when a right atrial myxoma causes a tricuspid valve obstruction to blood flow.^[1]