Almost 1% of all baby's is born with a heart defect (CHD) and most of them survive. Even though outcomes are good, they need lifelong follow-up because of a higher risk for cardiovascular diseases. Studies have shown that patients with CHD are not active enough and that a substantial amount of patients is overweight. Hence preventive strategies and education should not only focus on the heart problem, but also on a healthy lifestyle including physical activity. Recently a new guideline introduced exercise prescription based on the absence/presence of certain key elements. However, a number of important questions remain that preclude implementation in clinical practice. Therefore a 'Start-to-Sport' program for adults with CHD, based on this new guideline, will be investigated. This study is a randomized controlled trial that investigates the effects of the program on daily physical activity, exercise capacity, quality of life and exercise self-efficacy both in short (12 weeks) and long (52 weeks) term, along with possible mechanisms for the training effects by using a new exercise-testing protocol that looks simultaneously to all body parts that are involved during exercise. Ultimately, our findings will result in the implementation of the guideline in clinical practice.

Inclusion Criteria:

• adolescents and adults with congenital heart disease
• 16 to 65 years

Exclusion Criteria:

• congenital rhythm or conduction disorders
• isolated congenital coronary artery anomalies
• pregnancy
• being listed for heart transplantation
• inability to perform standard physical activities due to mental/physical disability.