Systolic ejection murmurs of the left heart usually have their peak during early to mid-systole. Few reports have addressed ejection murmurs with their peak at late systole. We evaluated the clinical significance of an apical systolic ejection murmur with a peak intensity during late systole using Doppler and two-dimensional (2-D) echocardiography and phonocardiography. The apical late systolic ejection murmur was observed in 9 of 13 consecutive patients with mid-left ventricular obstruction. We investigated the ejection flow velocity and the timing of maximum velocity at the three different sites of the left ventricle, the left ventricular cavity shape, and the timing of the peak murmur intensity in these nine patients (late-murmur group). The same parameters were also examined in 8 consecutive patients with mid-systolic ejection murmurs (mid-murmur group), 10 with early systolic ejection murmurs (early-murmur group), and 7 controls without murmurs. Patients with aortic stenosis were excluded. The mid-ventricular ejection flow velocity was significantly higher in the late-murmur group than in the other three groups; that of the outflow tract was markedly higher in the mid-murmur group. The ejection flow velocity at the aortic orifice of patients in the early-murmur group was significantly high compared with that of the controls. The timing of the peak murmur intensity in each group correlated with that of the peak flow signal at the corresponding site with maximum velocity. In all patients in the late-murmur group, 2-D echocardiography revealed a systolic narrowing of the cavity at the mid-ventricle. Amyl nitrite inhalation induced a marked increase in the intensity of the murmur without evidence of appearing or increasing mitral regurgitation. It was concluded that the apical ejection murmur with a late systolic peak intensity is a new phonocardiographic sign indicative of dynamic, mid-left ventricular obstruction. This murmur should be differentiated from the mitral regurgitant murmur.