In Pediatric Cardiology for many years the usage of spironolactone (Aldactone) and Canreonat-K+ (Aldactone pro injectione) had been experienced. The efficiency of aldactone was controlled by clinical parameters, electrolytes, discontinuity of the drug and in some cases by radioimmunologic measurement of the plasma aldosterone concentration. The treatment with aldactone in combination with digitalis gave good clinical results in cases with and without signs of secondary hyperaldosteronism. The recommended dosage i. v. and orally was for infancy 2--3 mg/kg/die the first 2--4 days and afterwards 1,5--2 mg/kg/die, for later childhood 4--5 mg/kg/die for 3--5 days and afterwards 2--3 mg/kg/die. Special attention should be paid to hyperkaliemia, over 6 mval serum K+ the aldactone administration was interrupted.