The authors evaluated some renal functional parameters of 23 children, the ages ranged 1 to 58 weeks; 8 were affected with cyanotic congenital heart disease and 15 with acyanotic forms. They showed the presence, already in this age, of some affections that are quiet similar to those affecting older children with heart disease. They tried to explain the renal functional deficiency in consideration of the literature data also. The authors formed a functional deficiency greater in the cyanotic forms, proportional to the weight deficiency and the same as that described in dystrophic children. They think that this is due to a first year maturational retardation, because of a low trophism of the body, in particular of the kidney. The authors suggest that these patients have to be fed with appropriate caloric-protein diet.