To plan the treatment of congenital heart malformations, a detailed knowledge of anatomy and hemodynamics is essential. This has previously been obtained by heart catheterization and angiocardiography. During the past 20 years, several non-invasive techniques, such as echocardiography with Doppler, magnetic resonance imaging and isotope techniques have evolved. They have profoundly changed the way we practise pediatric cardiology. For the initial investigation of a patient with suspected heart disease, echocardiography is the routine method. For the less experienced, tele-transmission to a pediatric cardiology center can be used to complement to investigation. In the preoperative investigation, echocardiography with Doppler plays an important role. In some situations, such as aortic lesions or complex cardiac malformations, magnetic resonance imaging is useful. Isotope methods have been used mainly for quantification of the degree of left-to-right shunts. During a 5-year period, 695 infants and children were operated on for a heart malformation: 40% were operated on without previous heart catheterization. For patients needing surgery before 1 month of age, 58% could be operated on based on non-invasive data alone.