Angiotensin convertase inhibitor (Enalapril) was used in 51 children aged 4 days up to 18 years (mean 4.3 +/- 5.5, years). As many as 27 subjects were newborns (4) and infants (23). The patients suffered from circulatory insufficiency due to congestive cardiomyopathy (13 cases). 6 treated subjects suffered from circulatory insufficiency due to congenital heart malformations before cardiac surgery and 22 after it (including complex malformations operated according to Fontan method). 10 children were treated because of arterial hypertension. 4 subjects suffered form life-threatening arrhythmias coexisting with circulatory insufficiency.