The effect of verapamil on left ventricular diastolic function in coronary artery disease was assessed by Doppler echocardiography of transmitral flow velocities in 20 patients. At baseline, isovolumic relaxation time was prolonged compared with that in 18 age-matched normal subjects (95 +/- 13 msec versus 74 +/- 12 msec, p less than 0.001), but decreased to 80 +/- 14 msec (p less than 0.001) after treatment. The ratio between early and atrial-induced transmitral velocities (E/A-ratio) at baseline was lower in patients than in normal subjects (1.1 +/- 0.2 versus 1.4 +/- 0.3, p = 0.01), as was the filling fraction of the first third of diastole (43% +/- 5% versus 50% +/- 4%, p less than 0.001). Verapamil treatment increased the E/A-ratio to 1.3 +/- 0.4 (p less than 0.001) and filling fraction to 45% +/- 4% (p = 0.055) because of increased early filling. No change in systolic performance or heart rate was observed. Thus, coronary artery disease was associated with retarded relaxation and impairment of early filling. However, verapamil treatment enhanced relaxation and induced a filling shift toward early diastole, which indicated improved diastolic performance. The changes probably reflected reduced myocardial ischemia.