Selective inhibition of sinus node function offers the possibility to decrease heart rate and reduce myocardial oxygen consumption in patients with impaired cardiac function, if myocardial contractility is not further attenuated. To study the influence of a specific sinus node inhibitor on myocardial function, alinidine was given to 10 patients with chronic congestive heart failure and stable sinus rhythm. Radionuclide ventriculography was used to monitor left ventricular function at rest and during a standardized exercise protocol. After a bolus injection of 45 mg of alinidine followed by infusion of 10 mg/hr, radionuclide studies were repeated 1.5 and 3 hours later. The results show that left ventricular ejection fraction, stroke volume, and end-diastolic volume index were essentially unchanged, whereas cardiac index decreased by 10% at rest and during exercise. Heart rate decreased markedly by 14% at rest and by 13% during exercise. Systolic blood pressure was reduced by 6% at rest and by 14% during exercise. As a result of the marked decrease of these two parameters, a pronounced effect was seen on rate-pressure product with a 19% decrease at rest and a 24% decrease during exercise. No significant side effects were observed. Alinidine might be given to patients with chronic congestive heart failure and sinus rhythm in doses up to 45 mg without exerting a clinically relevant negative inotropic effect. Therefore it may represent an alternative to other drugs when a decrease in heart rate is desired to reduce myocardial oxygen consumption.