Transseptal puncture (TSP) is a standard procedure to obtain access to the left heart. However, data on TSP in infants and children particularly with congenital heart defects (CHD) is sparse. Safety and efficacy of TSP in infants and children 1 year) who was discharged well later. Minor complications emerged in 5 patients. The youngest of these individuals (0.3 years, 5.8 kg) developed small pericardial effusion after anterograde ballon valvuloplasty for critical aortic stenosis. The remaining 4/5 patients developed small pericardial effusion after ablation of a left-sided accessory atrioventricular pathway (6.1–12.2 years, 15.6–34.0 kg). TSP for access to the left heart was safe and effective in children and adolescents > 1 year of age. However, TSP was a high-risk procedure in small infants with a restrictive interatrial septum with need for enlargement of interatrial communication.