Induction and maintenance of anesthesia with high-dose fentanyl and oxygen cause minimal changes in cardiovascular dynamics in patients with mitral valvular disease, and in those undergoing surgery for myocardial revascularization. Fentanyl at 10 .mu.g/kg did not significantly change any cardiovascular variable studied and at 20 .mu.g/kg produced a significant decrease in heart rate and mean arterial pressure without affecting stroke volume, cardiac output, central venous pressure or peripheral vascular resistance. One of the frequently reported disadvantages of fentanyl is the development of chest and abdominal wall rigidity. In a series of 359 patients, 285 (79.4%) developed this complication following an infusion of 8.8 .mu.g/kg administered over a period of 1 min, resulting in slight to total inability to inflate the chest. Comstock et al., using 200 .mu.g/min fentanyl, reported a high incidence of rigidity associated with hypercarbia, and Kentor et al., using 50 .mu.g/kg infused over 60 s, reported 100% occurrence of rigidity. Stanley, infusing 50-200 .mu.g/kg fentanyl, reported no incidence of rigidity. Lunn et al., using 300 .mu.g/min fentanyl, reported a small reduction in chest wall compliance which did not impair ventilation. In view of these conflicting reports and the clinical impression that rigidity frequently occurs, the following study was designed to establish the incidence of rigidity with high-dose fentanyl-oxygen induction of anesthesia; to assess the efficacy of a simultaneous infusion of pancuronium in preventing rigidity; and to compare the hemodynamic effect of i.v. fentanyl alone to that of fentanyl with a stimultaneous infusion of pancuronium.