To explore underlying mechanisms and clinical implications of middiastolic filling, we measured early and late mitral inflow velocities, deceleration time of early mitral inflow velocity, and early diastolic mitral annular velocity (E′) recorded by pulsed wave Doppler echocardiography in 3 cardiac cycles of 35 patients with prominent mitral inflow (middiastolic flow velocity ≥ 0.2 m/s). E′ was measured at the septal corner of the mitral annulus by Doppler tissue echocardiography from the apical 4-chamber view and was found to be reduced (E′ < 0.1 m/s) in all patients; early mitral inflow velocity/E′ ratio was > 10 in all but 1 patient. Valsalva maneuver unmasked delayed relaxation in 15 (88%) of 17 patients and abolished middiastolic filling in 10 (59%). Triphasic mitral inflow with middiastolic flow is related to elevated filling pressure, delayed myocardial relaxation, and slow heart rate, indicating advanced diastolic dysfunction.