Cardiac transplantation is predicted to improve survival for patients with severe symptoms of heart failure and ejection fraction of 20% or less, but the exercise capacity after cardiac transplantation is less than normal. Patients responding to vasodilators and diuretics have progressive improvement in exercise capacity despite low ejection fraction. We hypothesized that among patients currently considered appropriate for transplantation who could nonetheless subsequently be stabilized on medical therapy tailored to hemodynamic goals, survivors after 6 months of sustained medical therapy would demonstrate exercise capacity comparable to that of survivors of transplantation. Of 146 patients referred, 118 (81%) were discharged on tailored therapy without transplantation, and 88 (60%) were stable for at least 1 month. Stability after discharge was more likely in patients with lower right atrial pressures and better renal function on therapy. Of the 88 stable patients, 45 patients were listed for transplant, and 43 were ineligible or unwilling. From these patients, 42 survivors for more than 6 months follow-up after cardiac transplantation or tailoring of medical therapy underwent exercise testing. Baseline functional and hemodynamic status and left ventricular ejection fraction (15 +/- 4%) were not different between the transplant and sustained medical survivor groups at the time of initial evaluation. After 14 +/- 6 months, left ventricular ejection fraction had increased to 62 +/- 7% after transplantation (p less than 0.01) and only 22 +/- 9% after sustained medical therapy (p less than 0.05). However, there were no significant differences in the maximum workload, oxygen uptake, anaerobic threshold, or maximum oxygen pulse between survivors of cardiac transplantation and survivors on sustained medical therapy.(ABSTRACT TRUNCATED AT 250 WORDS)