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To assess the acute cardiovascular effects of cimetidine--a widely used histamine-H(2)-receptor antagonist--cuff arterial blood pressure, M-mode echocardiogram of the left ventricle and systolic time intervals were recorded in 10 healthy volunteers before and after 200 mg of cimetidine or isotonic saline given intravenously in a double-blind cross-over manner. Neither echocardiograms nor systolic time intervals revealed any significant effects of cimetidine on the left ventricular performance. However, cimetidine decreased slightly the systolic arterial pressure. The maximal effect of cimetidine (7 +/- 1 mmHg, mean +/- SEM) differed significantly from that of saline (3 +/- 1 mmHg, p less than 0.02). When compared with the pre-injection level, the calculated total peripheral resistance decreased significantly after cimetidine (p less than 0.01), whereas saline induced no such change. We conclude that a bolus injection of cimetidine does not impair cardiac performance but may induce transient hypotension due to reduction of the total peripheral resistance. This reduction can explain the hypotensive effect of i.v. cimetidine reported in acutely ill patients.