This study was designed to evaluate the impact of antihypertensive therapy on cardiac dysrhythmias in 13 hypertensive patients who received calcium entry blockers and in 10 hypertensive patients who received hydrochlorothiazide. Mean arterial pressure fell to a similar extent in both treatment groups; however, left ventricular mass index decreased (from 102 +/- 4 to 95 +/- 2 g/m2) only in patients receiving calcium entry blockers, but not in those taking hydrochlorothiazide. The prevalence of premature ventricular contractions decreased 74% from 21 +/- 14/h to 5.7 +/- 6/h in the calcium entry blocker group, but did not change in the hydrochlorothiazide group (15 +/- 17/h to 16 +/- 13/h). Couplets, multiform contractions, ventricular tachycardia, and supraventricular tachycardia were completely abolished after calcium entry blocker therapy, whereas the prevalence of these arrhythmias remained unchanged during treatment with hydrochlorothiazide. We conclude that antihypertensive therapy with calcium entry blockers (but not with thiazide diuretics) reduces left ventricular mass and the prevalence and severity of ventricular dysrhythmias. Whether this reduction will improve the ominous prognosis of left ventricular hypertrophy and diminish the risk of sudden death remains unknown.