HEART failure is associated with an inability of the heart to empty itself adequately, with the result that there is a high venous filling pressure and a decrease in the effective work done by the heart muscle. There are several factors that, if sufficiently severe, will produce congestive heart failure in either infancy or childhood. These include valvular obstruction or insufficiency; mechanical obstruction of the heart as a whole, as in pericardial disease; the physical effects of large intracardiac shunts which increase the load on one or both ventricles; the presence of raised pressure in the pulmonary or systemic circulation; inflammatory reactions in the heart muscle or oxygen lack; and, finally, certain metabolic disturbances, such as hyperthyroidism or hypothyroidism. One or more of these factors may be operating in the same child, as in rheumatic fever where myocarditis is associated with valvular insufficiency, or in congenital heart disease with pulmonary stenosis and patent foramen ovale, where the right ventricle has a high pressure to maintain and is at the same time being offered cyanotic blood from the coronaries. PATIENT MATERIAL In analyzing 1,580 cases of congenital heart disease at the Hospital for Sick Children, Toronto, 20 per cent were found to have had failure at some time. In 90 per cent of these failure occurred in the first year of life. A list of the various causes of heart failure in the pediatric age group in order of frequency follows. [see table in source pdf] In certain types of heart defects failure develops in characteristic age groups. For example, during the first week of life the most common cause of heart failure is aortic atresia. From 1 week to 1 month, coarctation of the aorta leads. From 1 to 2 months, transposition of the great vessels predominates. From 2 to 3 months, endocardial fibroelastosis is the chief cause of heart failure, with transportation of the great vessels second to it. The actual incidence of type of heart defect in relation to age at onset of heart failure is as follows.