This study was performed to investigate the characteristics of isovolumic relaxation flow velocity (IRFV) in the mid-portion of the left ventricle. Doppler examinations were performed at rest in 20 subjects with normal heart and 18 with hypertrophic heart disease. To assess the left ventricular flow conditions in hyperdynamic states, 10 healthy subjects underwent exercise Doppler echocardiography. From the apical transducer position, left ventricular filling velocities were obtained at the mitral valve orifice level and at the mid-ventricle, and the changes of peak velocities in the rapid filling (R0, R1) and atrial contraction phases (A0, A1) were measured [%R = (R1-R0)/R0, %A = (A1-A0)/A0]. There was a good correlation between IRFV and %R (IRFV = 0.69 X %R + 25.9, r = 0.75, p less than 0.001). However, there was no correlation between IRFV and %A. Prominent IRFV (greater than or equal to 30 cm/sec) was demonstrated in 13 subjects, including 10 with hypertrophic heart disease. During exercise, IRFV, %R and %A did not increase. It was concluded that a prominent IRFV was associated with the acceleration of rapid filling velocity at the mid-ventricle. This phenomenon may be caused by regional and asynchronous hyperdynamic states demonstrated in hypertrophic heart disease.