Perioperative spasm of the internal mammary artery (IMA) may occur after coronary artery bypass surgery. Diltiazem is often used to prevent it. We studied the haemodynamic tolerance of this drug just after coronary artery bypass surgery, using an intravenous injection of 0.3 mg.kg-1 in 2 minutes. Fifteen patients were studied and the injection was performed less than one hour after the arrival of the patient in the intensive care unit. A reduction in systemic arterial blood pressure and a negative chronotropic effect was observed. There was no significant modification of cardiac output. Diltiazem used in that context has no myocardial depressant effect.