The hemodynamic and pharmacokinetic effects of the novel class 1c antiarrhythmic drug restacorin were investigated in two groups of patients. Group I consisted of 5 patients with normal left ventricular (LV) function, and group II consisted of 10 patients with mild heart failure [New York Heart Association (NYHA) II; mean LV ejection fraction 33 +/- 6%]. The study had an open label, baseline-controlled, single-dose design. Restacorin was infused in a total dosage of 1.2 mg/kg. In group I, the only significant change as compared with baseline findings was a 25% increase in right atrial pressure. In group II; cardiac output (CO), dP/dt, and stroke work index (SWI) decreased significantly (-18, -11, and -24%, respectively). In addition, a significant 32% increase was noted in pulmonary artery wedge pressure (PAWP), and a 27% increase occurred in systemic vascular resistance (SVR). No changes were observed in heart rate (HR) or mean arterial blood pressure (MAP). CO and SVR at baseline correlated with the average plasma concentrations (r = -0.65 and p = 0.009 and r = 0.56 and p = 0.028 respectively). Creatinine clearance was inversely correlated to the restacorin plasma concentration (r = -0.51, p = 0.05). The half-life (t1/2) elimination time of restacorin was 2.60 h for group I, and 4.06 h for group II. Clearance was 51.4 and 32.2 L.h-1, respectively. Restacorin appears to be well tolerated in patients with normal LV function. The drug is not recommended for use in patients with reduced LV function because of its moderate negative inotropic effect.