Left ventricular diastolic function before and after the administration of disopyramide (100 mg) or diltiazem (30 mg) was assessed in 10 patients with nonobstructive type hypertrophic cardiomyopathy. Left ventricular diastolic function was assessed by Doppler echocardiography. The peak early (E) and late (A) diastolic flow velocities and E/A ratio (E/A) were measured. Three hours after the administration of disopyramide, blood pressure did not significantly change, but heart rate was decreased significantly (p less than 0.01). Disopyramide increased the E velocity and E/A ratio from 43.8 +/- 15.0 cm/sec to 51.3 +/- 16.1 cm/sec and from 0.71 +/- 0.20 to 1.00 +/- 0.24 (each p less than 0.01), respectively, and decreased the A velocity from 63.9 +/- 18.5 cm/sec to 52.1 +/- 14.9 cm/sec (p less than 0.01). Diltiazem increased the E velocity and E/A ratio from 42.8 +/- 12.5 cm/sec to 46.4 +/- 13.4 cm/sec (p less than 0.05) and from 0.74 +/- 0.21 to 0.96 +/- 0.28 (p less than 0.01), respectively, and decreased the A velocity from 60.6 +/- 16.4 cm/sec to 50.2 +/- 15.6 cm/sec (p less than 0.01). These results indicate that disopyramide improved left ventricular diastolic filling in hypertrophic cardiomyopathy, and its effect was similar to that of diltiazem.