The objective of this prospective study was to determine the nocturnal/diurnal distribution of perioperative cardiac dysrhythmias in patients with coronary artery disease undergoing major vascular surgery. Eight patients with significant coronary artery disease undergoing major vascular surgery were studied. Continuous Holter monitoring was performed on each patient from approximately 1 h pre-operatively until 2-5 days post-operatively. Frequencies of isolated supraventricular and ventricular premature beats, and runs of supraventricular and ventricular premature beats were calculated for 6-h periods (00.00-06.00; 06.00-12.00; 12.00-18.00; 18.00-24.00 hours). Supraventricular tachycardia occurred significantly more frequently between 00.00 and 06.00 hours than during the other 6-h periods studied in the post-operative period following major vascular surgery.