Fifteen elderly patients with normal left ventricular (LV) systolic function and New York Heart Association functional class II-III were studied. The effect of verapamil on LV diastolic function was assessed by congestive heart failure (CHF) score, treadmill exercise test, and Doppler echocardiography at baseline, and after each three-month treatment period (placebo or verapamil 120 mg once daily), separated by a one-week washout period before crossover. Blood pressure, heart rate, LV ejection fraction, LV mass, and cardiac output were unaltered by placebo or verapamil. Verapamil treatment significantly improved CHF score at 3 months (3.5 +/- 0.5, p<0.05) compared with baseline (5.6 +/- 0.5) or placebo (5.5 +/- 0.5). The exercise time was similar at baseline (7.4 +/- 1.2 min) and after placebo (7.4 +/- 1.3 min) treatment but significantly (p<0.05) increased after verapamil (8.3 +/- 1.2 min) treatment. The ratio of mitral A wave duration/pulmonary venous atrial systolic reversal duration increased after verapamil (1.11 +/- 0.08) treatment compared with placebo (0.91 +/- 0.07, p<0.05) and baseline (0.89 +/- 0.08) which had similar durations. The isovolumic relaxation time was significantly (p<0.05) decreased from 84 +/- 12 ms at baseline and 86 +/- 13 ms with placebo to 73 +/- 9 ms with verapamil. The results of this study suggest that in elderly patients with Doppler evidence of diastolic dysfunction as the cause of CHF, three months treatment with verapamil can improve CHF, increase exercise tolerance and improve LV diastolic function.