Over the period from January 1982 to June 1989 the authors examined 1723 children and adolescents with congenital heart diseases (CHD), hospitalized in the Institute of Cardiovascular Diseases in Bratislava. Of these patients, 96 (5.6%) had CHD of primarily genetic etiology: monogenic diseases 51 (3%), chromosomal anomalies 45 (2.6%) patients. In indicated cases (polystigmatization, positive family history) the relatives were examined. Echocardiographic examination of 203 relatives of patients with genetically determined CHD yielded positive echocardiographic findings in 32 subjects (15.5%). In relatives of patients with CHD of primarily genetic etiology, even structural changes which hemodynamically are not severe may be of value for individuals who are carriers of pathologic genetic information. Echocardiography is a contribution not only to diagnosis but also to prevention of CHD in association with adequate genetic counselling. (Tab. 4, Ref. 7.)