Isovolumic relaxation sound: a new class of added heart sound?

An early diastolic sound in a patient with apical left ventricular disease is reported. Pulsed Doppler echocardiography showed blood flow within the left ventricular cavity during the isovolumic relaxation period whose peak flow velocity was synchronous with the onset of this diastolic sound. Because it occurred before filling started it could not have been either a third or fourth heart sound. It must thus represent a distinct and apparently unrecognised class of diastolic sound.