Compared to end-stage heart failure, a patient's situation is usually greatly improved after a heart transplant (HTx), but the exercise capacity remains sub-normal, also long-term, ranging from 50 to 70% in most studies. While effective rehabilitation, including regular exercise, is considered an effective tool of improving health related quality of life (HRQoL) and prognosis of cardiac patients in general, the knowledge about and the effect of different rehabilitation programs among HTx recipients is limited. Exercise training is considered one of the most central parts in rehabilitation, but the mode of exercise used in different studies varies considerably. It is documented that high intensity interval training (HIT) has superior effects compared to training with moderate intensity in cardiac and heart failure patients. In contrast, HTx recipients have a denervated heart, and HIT had been considered unphysiological. However, the investigators have recently demonstrated highly beneficial effects on exercise capacity, muscle strength, body composition, reduced progression of cardiac allograft vasculopathy and HRQoL among long-term HTx recipients. In the present study the investigators want to test the hypothesis that systematic aerobic exercise with high intensity improve exercise capacity also in newly transplanted recipients, and secondarily that it gives favourable effects on the heart, peripheral circulation and a better HRQoL.

Inclusion Criteria:

• Clinically stable HTx recipients approximately 8-12 weeks after HTx.
• Age > 18 years, both sexes
• Received immunosuppressive therapy as per local protocol.
• Patient willing and capable of giving written informed consent for study participation and anticipated to be able to participate in the study for 9- 12 months.

Exclusion Criteria:

• Unstable condition or postoperative complications
• Recent severe rejection episodes
• Physical disabilities which prevent participation
• Other diseases or disabilities that contradict/refrain from exercise.