OBJECTIVE To investigate the effects of IV infusion of atrial natriuretic peptide (human ANP 1-28) on renal function in patients with acute heart failure and renal impairment after cardiac surgery. METHODS Pharmocodynamic dose-effect investigation. METHODS Cardiothoracic Intensive Care Unit of a university hospital. METHODS Twelve patients (mean age 68 years, range 44-78 years) treated with inotropic drugs and an intra-aortic balloon pump (n = 8) were studied 1-3 days after cardiac surgery. Patients had acute renal impairment, defined as a rise in serum creatinine of more than 50% compared to preoperative values. Patients were receiving dopamine and furosemide infusion to increase urine flow. METHODS Baseline measurements of glomerular filtration rate (GFR) and renal blood flow (51Cr-EDTA and PAH clearance) were first performed during two 30-min periods. ANP was then administered for two consecutive 30-min periods (25 and 50 ng/kg per min), followed by two control periods. RESULTS Mean arterial pressure decreased by 6% at the highest ANP dose. Urine flow, GFR and RBF increased 62%, 43% and 38%, respectively, while renal vascular resistance decreased 30%. At this dose level, circulating ANP concentrations were on the average eight fold higher than preinfusion levels. CONCLUSIONS ANP improved renal function and decreased elevated renal vascular resistance in patients with renal dysfunction after cardiac surgery. The improvement in renal blood flow and glomerular filtration rate may be of potential therapeutic value to prevent or treat exaggerated renal vasoconstriction in patients with acute renal impairment following cardiac surgery.