The present report compares the effects of isoproterenol (ISO), norepinephrine (NE), and phenylephrine (PH) on the mean arterial pressure (MAP) and reservoir volume (RV) during cardiopulmonary (CPB) in 16 patients undergoing coronary artery bypass grafting (CABG) who were treated preoperatively with oral nifedipine (10 to 40 mg, three times a day) and propranolol (40 to 60 mg, three times a day). The changes of RV and MAP were used as indices of the changes in venous capacitance and arterial resistance, respectively, produced by the adrenergic agonists. ISO, a beta-adrenergic agonist, decreased both MAP and RV. NE, which activates both alpha 1- and alpha 2- adrenoceptors, increased both MAP and RV, while PH, a selective alpha 1-adrenergic agonist, increased only MAP with no significant change in RV. The changes are qualitatively similar to those previously achieved in patients undergoing valve replacement who did not receive any blocker preoperatively. However, the decrease of MAP by ISO and its increase by NE were significantly less in the CABG group. It is concluded that preoperative preparation of patients undergoing CABG with beta-adrenergic blockers and calcium channel blockers can modify the effect of ISO and NE on the peripheral resistance, but they have no significant effect on the action of PH at the doses selected in this study.