Although previous reports have attributed acute renal failure (ARF) following cardiovascular surgery to acute tubular necrosis (ATN), little emphasis has been placed on renal failure due to congestive heart failure (CARF). Of 100 cases of ARF studied prospectively over an 18-month period, 36 occurred after open-heart surgery. Nineteen of these cases were associated with heart failure. The remaining 17 had ATN as manifested by high urinary sodium, low urine/plasma creatinine, and abnormal urinary sediment. At the onset of CARF, intravascular volume expansion was universally present, and oliguria with pulmonary edema was common. Urinary chemistries were (mean +/- SD): sodium (mEq/L) 8 +/- 7, U/P creatinine 72 +/- 45, and FENa (%) 0.1 +/- 0.1. Therapy consisted of digoxin, furosemide (F), vasopressors (V), and, when indicated, intraaortic balloon counterpulsation. Survivors of CARF responded more frequently to F and required less V. Ultimately, survival depended upon improvement in cardiac performance. All oliguric ATN patients failed to respond to F. Mortality for the CARF group was 52%. In contrast, 82% of the oliguric ATN group expired, whereas overall ATN mortality was 60%. Cardiogenic acute renal failure is a frequent cause of ARF after open-heart surgery in our institution. It is characterized by prerenal urinary chemistries, has a high mortality, and may be reversible.