Vecuronium is a new nondepolarizing muscle relaxant which has been shown to cause no significant cardiovascular effects. Utilizing invasive monitoring in patients undergoing coronary artery bypass grafting, the authors compared the cardiovascular effects of vecuronium (0.28 mg/kg) in seven anesthetized patients with those of pancuronium (0.1 mg/kg) in five anesthetized patients. This dose of pancuronium represents three times its ED90 (dose producing a 90% depression of evoked twitch tension), while the vecuronium dose represents twelve times its ED90. This relatively large dose of vecuronium was chosen deliberately in an attempt to manifest any possible cardiovascular effects. Following administration of vecuronium, cardiac output increased 9% and systemic vascular resistance decreased 12%, while pancuronium produced a significantly greater 17% increase in cardiac output without change in systemic vascular resistance. Heart rate and systemic mean arterial pressure did not change following vecuronium, while increasing 22% and 24%, respectively, following pancuronium. The authors conclude that large doses of vecuronium have minimal cardiovascular effects and thus offer an advantage over pancuronium in patients anesthetized for coronary artery surgery.