Interventional catheter therapy has drastically changed the practice of cardiac catheterization and the treatment of congenital heart disease. In some centers, interventions amount to 30% or more of all cardiac catheterizations. For some lesions, surgery has become obsolete. For valvular pulmonary stenosis, balloon dilatation is the therapy of choice and results in permanent elimination of pressure gradients. Balloon dilatation is also indicated for valvular aortic stenosis and results in mild residual stenosis with gradients below 35 mmHg. Aortic insufficiency, mostly mild, is induced in 15%-20%. Native and post-operative coarctation can be successfully dilated. About 50% of pulmonary artery stenoses can be relieved by balloon dilatation. Stent placement increases the success rate to 75%-80%. Stent implantation is also being investigated for other lesions. Valvular pulmonary atresia can be opened by catheter technique. In the majority of patients over 6 kg, the patent ductus arteriosus is transvenously closed by implantation of the Rashkind occluder. Secundum or similar atrial septal defects and muscular ventricular septal defects can also be closed by catheter technique, but suitable specific occluders are not generally available at present. Therapeutic vascular occlusions, radiofrequency ablation of aberrant conduction pathways and arrhythmia foci are examples of other catheter interventions.