By idiopathic enlargement of the heart is meant an enlargement of the entire organ or parts of it which cannot be explained on a pathologic basis. I have found in the literature thirty-four cases reported as such which are accompanied by pathologic reports. In five of these, anomalies or abnormalities of the heart necessarily precluded their consideration as instances of idiopathic enlargement. In another case, the kidneys were twice the normal size, and while the microscopic examination did not reveal definite abnormalities, this case too cannot be considered as idiopathic. In five of the remaining twenty-eight cases, histologic examination was not mentioned. In six more, the microscopic examination revealed pathologic conditions in the musculature, and these may not be considered as truly idiopathic.
There remain, then, only seventeen cases which on the basis of anatomic and histologic examinations may be considered as true idiopathic enlargement (hypertrophy) in infancy and in