The aim of this randomised controlled study was to determine whether an esmolol infusion affected the incidence of ST segment changes during weaning from intermittent positive pressure ventilation and tracheal extubation after coronary artery surgery. Thirty-one patients received an infusion of esmolol 0-300 microg x kg(-1) x min(-1) and 37 patients comprised the control group. ST segment changes were monitored using a continuous ambulatory surveillance system. The electrocardiogram, direct arterial pressure and pulse oximetry were monitored continuously. The period of analysis was from 120 min before until 180 min after tracheal extubation. Three patients in the esmolol group developed myocardial ischaemia during the study period compared with 12 in the control group (p = 0.05). Heart rate increased with time during the study period (p = 0.002) in the control group but was unchanged in the esmolol group. Mean heart rate was significantly higher in the control group than in the esmolol group from 40 min before until 180 min after tracheal extubation. Seven patients in the esmolol group suffered adverse events related to the esmolol infusion. Although the use of esmolol reduced the incidence of myocardial ischaemia, the incidence of adverse effects makes it unsuitable prophylaxis for patients after coronary artery surgery.