We studied the effect of a calcium antagonist, diltiazem, on left ventricular (LV) diastolic performance of hypertrophied hearts in five patients (pts) with systemic hypertension (HHD) and 6 pts with hypertrophic cardiomyopathy (HCM) by a combined phonoechocardiographic technique. Data were analyzed before and after the oral administration of diltiazem (90-180 mg/day). In HHD, the prolonged LV isovolumic relaxation time, measured from the onset of the aortic component of the second heart sound to the beginning of the mitral valve opening, decreased significantly from 112 +/- 17 to 90 +/- 9 msec (p less than 0.01) and normalized LV peak filling rate during rapid filling phase increased in all pts without a statistic significance. This filling rate during atrial contraction phase decreased (1.61 +/- 0.59 to 0.93 +/- 0.22 sec-1, p less than 0.05). In HCM, LV isovolumic relaxation time and normalized LV peak filling rate during rapid filling phase showed no significant change, although normalized LV peak filling rate during atrial contraction phase decreased significantly (1.20 +/- 0.27 to 1.05 +/- 0.24 sec-1, p less than 0.05). In both pts groups, no significant changes were observed in R-R interval, systolic blood pressure, LV end-systolic dimension, end-diastolic dimension and fractional shortening of the LV minor axis before and after the administration of diltiazem. These data indicate that diltiazem shortens abnormally prolonged LV diastolic relaxation time and improves LV diastolic filling in pts with HHD, whereas diltiazem failes to show such effects in pts with HCM except for a decrease in the normalized LV peak filling rate during atrial contraction phase.