About 40% of children born with congenital heart disease die within the first year of life unless treated surgically. The results of surgery have improved with increasing experience. Currently, the mortality rate of open-heart procedures performed during the first year of life have decreased to about 25%. The present study analyses the causes of death in 53 infants who underwent open heart surgery at the Hospital for Sick Children, Great Ormond Street, London between 1973--1977. Fifty-three deaths represented 25% of the total 212 operated infants. Causes of death and possible contributing factors are discussed under the following headings: Inoperable lesions (18), poor preoperative condition (8), mistake in pre-, intra- and postoperative management (15), infection (2) and unclear (10). It is suggested that earlier diagnosis and operation may improve the results. The purpose of this study was to identify problems in the management of critically ill infants with congenital heart disease and thus improve their prognosis in future.