['We examined whether heparin-coated (HC) circuits can improve the operative results in patients with chronic renal insufficiency.', 'Elective cardiac surgery was performed in 24 patients with a serum creatinine (Cr) level of at least 1.5 mg/dl. Uncoated circuits were used in 12 patients, and HC circuits were used in 12 patients. The results of surgery were compared between the two groups.', 'The mean preoperative Cr concentration was significantly higher in the HC group (2.3 vs 1.8 mg/dl). The heparin doses, protamine dose, and activated clotting times were significantly lower in the HC group. The mean blood loss was also less, although this difference was not significant. The postoperative increase in the Cr level was small in the HC group (2.3-->2.5 mg/dl) compared to that in the noncoated group (1.8-->2.3 mg/dl). Postoperative dialysis was not required in the 5 patients in the HC group with a preoperative Cr clearance less than 20 ml/min.'] Do heparin-coated circuits prevent renal dysfunction after open heart surgery?