Value of peak exercise oxygen consumption for optimal timing of cardiac transplantation in ambulatory patients with heart failure. BACKGROUND. Optimal timing of cardiac transplantation in ambulatory patients with severe left ventricular dysfunction is often difficult. To determine whether measurement of peak oxygen consumption (VO2) during maximal exercise testing can be used to identify patients in whom transplantation can be safely deferred, we prospectively performed exercise testing on all ambulatory patients referred for transplant between October 1986 and December 1989. METHODS AND RESULTS. Patients were assigned into one of three groups on the basis of exercise data: Group 1 (n = 35) comprised patients accepted for transplant (VO2 less than or equal to 14 ml/kg/min); group 2 (n = 52) comprised patients considered too well for transplant (VO2 greater than 14 ml/kg/min); and group 3 (n = 27) comprised patients with low VO2 rejected for transplant due to noncardiac problems. All three groups were comparable in New York Heart Association functional class, ejection fraction, and cardiac index (p = NS). Pulmonary capillary wedge pressure was significantly lower in group 2 than in either group 1 or 3 (p less than 0.05), although there was wide overlap. Patients with preserved exercise capacity (group 2) had cumulative 1- and 2-year survival rates of 94% and 84%, which are equal to survival levels after transplantation. In contrast, patients rejected for transplant (group 3) had survival rates of only 47% at 1 year and 32% at 2 years, whereas patients awaiting transplantation (group 1) had a survival rate of 70% at 1 year (both p less than 0.005 versus patients with VO2 greater than 14 ml/kg/min). All deaths in group 2 were sudden. By univariate and multivariate analyses, peak VO2 was the best predictor of survival, with only pulmonary capillary wedge pressure providing additional prognostic information. CONCLUSIONS. These data suggest that cardiac transplantation can be safely deferred in ambulatory patients with severe left ventricular dysfunction and peak exercise VO2 of more than 14 ml/min/kg. 