The long-term influence of exercise training after heart transplantation remains unclear. Accordingly, we performed a 12-year follow-up study of 36 patients who underwent heart transplantation. Findings for survivors were compared with those of age-matched controls over the same period. Comparisons were also made between survivors and deceased patients. The sample comprised 36 men (aged 47 ± 9 years) and a group of healthy age-matched controls. The patients received 16 months of outpatient exercise training; physiologic data were collected initially and at discharge. At 12 years, further data were collected on 20 of 23 survivors and their controls; 3 of the survivors were unavailable for final assessment, and 13 patients had died in the interim. The survivors’ peak oxygen intake (V̇O_2peak) increased 26% after training and decreased 0.39 mlkg−1min−1 per year (27.9 ± 7 to 23.7 ± 6), which was a similar rate as the controls (0.37 mlkg−1min−1 per year; 33.7 ± 7 to 29.2 ± 7). Lean body mass (LBM) increased 3 kg by 16 months and a further 2.5 kg by 12 years, but ultimately was 3 kg below the controls. Although there was no difference in entry data between deceased patients and survivors, the latter attained greater gains in V̇O_2peak and LBM over the 16 months of training. Thus, in heart transplantation patients who undergo training, gains in exercise capacity are lost over 12 years at a rate commensurate with normal aging. A reduced training response in V̇O_2peak and LBM contributes to a poorer prognosis.