Histologic material from 450 cases of congenital cardiac malformations was reviewed for myocardial, endocardial, and coronary artery lesions. Myocardial necrosis, calcification, or scarring were found in 106 cases. The myocardial changes appeared to result from reduced coronary perfusion rather than oxygen desaturation. The most frequent involvement was seen in defects which cause hypoperfusion; aortic and pulmonary valve defects and anomalous origin of the left coronary artery. The changes in these cases were also the most acute and widespread. Similar lesions were found in congenital mitral stenosis in the absence of shunting defects. Myocardial lesions were infrequent in defects which result in arterial desaturation—transposition and tetralogy of Fallot. Significant coronary sclerosis was present in several types of malformation but was not always associated with myocardial lesions. Endocardial proliferation was found overlying myocardial scarring in some cases, but, in spite of its morphologic similarity, it could not be related to the coronary artery lesions.