The majority of children born with congenital heart disease survive to adulthood thanks to advances in pediatric cardiology and pediatric cardiac surgery in the last fifty years. At the moment, in Croatia there are about 10,000 children with congenital heart disease, which will survive into adulthood. This thesis is about most common cardiac diseases (atrial and ventricular septal defect, coarctation of the aorta, tetralogy of Fallot, transposition of great vessels and univentricular heart) and their characteristics before and after surgery as well as conditions in unoperated patients. Heart diseases such as atrial and ventricular septal defect and coarctation of the aorta can be diagnosed even in adulthood. These diseases in adult can be clinically manifested differently- from patients who have no symptoms to severe patients, and it depends on the nature of the defects and the results of treatment, the number and complexity of operations, and time of intervention. Regardless of the diversity, principle of monitoring, diagnosis and treatment are the same with only purpose, and that is maintaining cardiac function and better quality of life. The most common complications that occur in adults with congenital heart disease are arrhythmias, heart failure, systemic arterial hypertension and thromboembolism, and they require prevention and treatment. Prophylaxis of infective endocarditis should be administered only by strict criteria. This thesis provides guidelines that should be followed in monitoring these patients. Patients also face other problems – limitation of exercise and sport, family planning and pregnancy and social issues, such as guidance and health insurance. The aim of this paper is to draw attention to the transition of a large number of patients with congenital heart diseases into adulthood and large growing public-health problem.