To establish whether an intramural left anterior descending coronary artery (LADA) is a simple anatomic or a singularly pathologic variant we studied 39 hearts, each with an intramural course of the LADA and no coronary artery disease, valvular derangement, cardiomyopathy, or congenital anomaly. Seventeen of the 39 hearts had no myocardial lesions, while 22 had gross and/or microscopic alterations in the myocardial territory supplied by the intramural LADA. The myocardial lesions consisted of one or more of the following: interstitial fibrosis, replacement fibrosis, contraction band necrosis, and/or increased vascular density in areas of focal fibrosis. The coronary anatomy of the 22 hearts with myocardial lesions (group 1) was compared with that of the 17 hearts without myocardial changes (group 2). Each of the group 1 hearts had an intramural LADA deeply placed within the ventricular wall and attenuation of potential collateral blood flow because of a co-existing intramural course of the posterior descending artery, other epicardial coronary arteries, and/or a diminutive right coronary artery. The myocardial changes in group 1 hearts and their absence in group 2 hearts suggest that the deep, intramural LADA of the group 1 hearts is abnormal rather than a simple anatomic variant of normal. Furthermore, the deep intramural LADA may be associated with sudden death since 13 of the 22 group 1 hearts were from sudden death victims. Six of these 13 persons died suddenly during vigorous exercise.