Data are reported on 142 infants less than 3 months old who left the operating room alive after an open intracardiac operation during the 13 years from January 1967 to July 1980. The probability of postoperative in-hospital cardiac death for acute postoperative heart failure (the most common mode of death in these infants) was found by multivariate logistic analysis to be significantly related only to the strength of pedal pulses, the pedal skin temperature and the cardiac index in the first 5 postoperative hours. When cardiac index was not analyzed and cold cardioplegic myocardial preservation methods used, only pedal pulses and pedal skin temperature were significant predictors of hospital death. Blood pressure and heart rate were not related to this mode of hospital death. Oliguria occurred in 23 percent of patients; it was related primarily to inadequate cardiac performance and increased the probability of hospital death. Treatment protocols are derived based on these facts.