In an attempt to determine predictive factors of spontaneous death in patients needing heart transplantation, we studied 27 clinical and paraclinical variables in 171 patients aged from 14 to 61 years. Sixty-one of these patients died before transplantation could be performed, 59 were still alive awaiting transplantation and 51 received a heart transplant. The actuarial survival rate with or without transplantation was 65 percent at 1 year and 51 percent at 2 years. Univariate analysis showed that the following factors were associated with a higher mortality rate: age, history or symptoms of right heart failure, poor general condition, end-diastolic left ventricular diameter and ejection fraction. There was no correlation between high mortality rate and type of heart disease, sex, duration of symptoms, NYHA functional class, cardiothoracic ratio and data obtained from electrocardiography and right heart catheterization. At multivariate analysis (Cox's model), no variable could be selected as predictive factor of mortality. The natural outcome of patients needing heart transplantation therefore is globally unfavourable. This means that once has been decided to perform heart transplantation the operation should not be delayed.