The haemodynamic effects of a new antiarrhythmic drug quinacainol (RP 54272) were evaluated in 12 untreated patients with normal left ventricular function referred for diagnostic cardiac catheterisation. The haemodynamic data were obtained before, 5 and 25 minutes after the injection of the drug (0.21 mg/kg/min during 6 minutes). A slight decrease of cardiac contractility indexes was constantly observed: dp/dtmax decreased (-15%) in all patients (p less than 0.05), with no concomitant change of left ventricular pressure or left ventricular end diastolic volume with respect to control values. Cardiac output and left ventricular ejection fraction did not change significantly. Heart rate increased in all patients from 74.3 +/- 9.8 to 79.9 +/- 8.6 beats per minute after 5 minutes (paired t test p less than 0.05), and was 79.8 +/- 9.0 beats per minute after 25 minutes. Systemic arterial resistance increased in 7 patients due to a reflex adrenergic discharge. The interpretation of the haemodynamic data was difficult in 3 cases due to systemic vasodilatation, which was poorly tolerated in one patient. The contribution of vagolytic reaction and adrenergic reaction to the negative inotropic effects of the drug must be evaluated before giving in to patients with impaired left ventricular function.