Atrial natriuretic hormone is released from the right atrial appendage in response to atrial distention. During cardiac operations the right atrial appendage is usually partially removed or ligated for venous cannulation. To evaluate the effect of right atrial appendectomy on the release of atrial natriuretic hormone and its natriuretic and diuretic responses, we prospectively randomized into two groups 23 patients undergoing elective coronary artery bypass operations. There were 16 male and 7 female patients with a mean age of 62 +/- 7 years. Group A (n = 11) had the right atrial appendage removed, and group B (n = 12) had the right atrial appendage preserved and venous cannulation done lateral to the appendage. The two groups were comparable for sexual distribution, age, number of grafts, and extracorporeal bypass time. All patients had normal left ventricular and renal functions, and they did not receive any diuretics during the study period. The patients were studied both preoperatively and postoperatively whereby the atrial natriuretic hormone serum levels, urine volume per minute, fractional excretion of sodium, amount of sodium excreted, and central venous pressure were measured before and after volume expansion with 5% albumin, 7.5 ml/kg. There was no statistical difference in these parameters preoperatively. In the postoperative period, however, group B patients had higher atrial natriuretic hormone levels after volume expansion than group A patients (376 +/- 84 versus 184 +/- 31 pg/ml; p less than 0.05), higher urine volume per minute (4.4 +/- 1.0 versus 2.0 +/- 0.4 ml/min; p less than 0.05), higher fractional excretion of sodium (2.30 +/- 0.66 versus 0.64 +/- 0.19; p less than 0.02), and higher amount of sodium excreted (511.1 +/- 150.9 versus 83.9 +/- 22.8 mmol/min; p less than 0.02). The central venous pressure was similar both before (9 +/- 1 versus 9 +/- 1 mm Hg) and after (16 +/- 1 versus 15 +/- 1 mm Hg) volume expansion in both groups. We conclude that preserving the right atrial appendage during cardiac operations significantly increased the release of atrial natriuretic hormone, resulting in increased urinary sodium excretion and better diuresis in the postoperative period.