A survey of the literature reveals that under the heading "congenital idiopathic hypertropy of the heart" numerous pathologic conditions are included. In some of the cases the cause for the hypertrophy is known and therefore the cardiac enlargement should not be identified as "idiopathic." To this group in particular belong the cases of glycogen storage disease,1 cases of enlargement of the heart associated with hypertension 2 and cases of enlargement accompanying severe anemia.3 In a much larger number of cases, while the etiologic factors are not absolutely established, cardiovascular abnormalities and/or pathologic changes are reported which could have some causal relation to the cardiac hypertrophy. This group comprises cases in which there are anomalies of the great vessels,4 abnormalities of the origin and distribution of the coronary arteries,5 rhabdomyomas,6 myocardial degeneration and pericardial, endocardial and perivascular fibrosis.7 From the Department of Pediatrics and the Pathological