Observations have been carried out on 116 neonates and infants with congenital heart malformations, and cardiomyopathies; 75 of them died. The initial diagnosis was made at Maternity Hospitals or at Infants' Wards, mainly in county hospitals of the province of Gdańsk. Afterwards these children were sent to the pediatric cardiology ward of the Pediatric Institute in Gdańsk, where the diagnoses were verified. Catheterisation and angiocardiography were performed in 29 children; 18 patients were treated surgically due to operable heart malformations. Rashkind's balloon atrioseptostomy was performed in three infants. The diagnosis based on physical ECG and X-rays was correct in only 42% of cases, and was most accurate in children with transposition of the great arteries, syndrome of Fallot, coarctation of the aorta and ventricular septal defects. The greatest difficulties were caused by the cases with hypoplastic left heart syndrome, double outlet of the right ventricle, single ventricle. They suggested that the initial clinical diagnosis should be confirmed by hemodynamic data and angiocardiography.