Magnetic resonance imaging (MRI) allows a static and cinetic study of congenital heart diseases avoiding patient exposure to ionizing radiation. It allows for evaluating cardiac morphology, heart function with accurate ventricular volume estimation, flow quantification with gradient and regurgitant fraction estimation, and vascular anatomy (aortic, pulmonary and proximal coronary vessels). Computed tomography (CT), with greater spatial resolution, allows for evaluating proximal and distal coronary arteries, vascular and pericardial calcifications, metal structures such as stents and prosthetic valves. The use of MRI or CT in young and adult patients with congenital heart diseases should be assessed case by case through a close collaboration between cardiologists and radiologists, aiming at an optimal tradeoff between expected diagnostic gain and biological cost in terms of ionizing radiation exposure and contrast material administration.