This study was undertaken to determine the circulatory effects of metocurine (dimethyltubocurarine) in 7 men scheduled for coronary artery surgery who had been receiving propranolol for at least 6 weeks before morphine-N2O-O2 anesthesia. The study was divided into 4 measurement periods: (1) control after induction; (2) 5 minutes after administration of 0.35 mg/kg of metocurine; (3) 10 minutes after; (4) 20 minutes after. There were no significant changes in mean blood pressure, heart rate (HR) central venous pressure or arterial blood gases throughout the study. Cardiac index rose significantly from a control value of 1.89 +/- 0.1 L/min/m2 to 2.39 +/- 0.2 L/min/m2 in period 2 and remained elevated throughout (2.53 +/- 0.3 and 2.33 +/- 0.2 Lmin/m2). Systemic vascular resistance (SVR) fell from a control value of 20.2 +/- 1.8 units to 16.1 +/- 1.6 units in period 2 and remained below control in periods 3 and 4 (17.2 +/- 1.8 and 16.9 +/- 1.3). These data suggest that metocurine produced a significant decrease in SVR in the presence of propranolol, resulting in an increase in cardiac output (and stroke volume) in a compensated heart, to maintain perfusion pressure. The possibility of a central (cardiac) effect cannot be excluded, but the lack of an increase in HR suggests it would not be clinically significant.