Anomalous origin of the left coronary artery from the pulmonary trunk, though a discrete anatomic malformation, manifests a spectrum of clinical and pathologic consequences. The objectives of this study were to characterize the primary anatomic findings in a group of specimens with anomalous left coronary artery and the extent of secondary morphologic and pathologic changes. Although the cases studied probably represent the least favorable end of the spectrum, the observed pathogenesis and evolution of secondary changes suggest that reconstruction of a two-coronary arterial system supplied through two coronary arteries would be advantageous to most patients. A high origin of the right coronary artery or location of the left coronary artery adjacent to a pulmonary cusp or branch may complicate the tunnel-type repair. In these cases, transfer of the left coronary artery to the aorta may be preferable.