INTRODUCTION AND OBJECTIVES Retrograde aortocoronary dissection is an unusual complication of coronary angioplasty. Our study provides new structural details of the aortic sinuses and the proximal portions of the coronary arteries, which enable better understanding of several clinical features associated with this complication. METHODS We studied eight aortic sinus specimens from patients with structural ischemic heart disease using dissection, histologic analysis, and scanning electron microscopy, and compared findings with those in eight control specimens. RESULTS We observed the following features: a) in 10 specimens (71%), the left coronary artery diameter was greater than the right; b) the angle that the ascending aorta made with the left coronary artery was acute, whereas that with the right coronary artery was closer to a right angle, thereby possibly providing a better approach for catheterization; c) in contrast to those of the right coronary artery, the periostial wall and sinotubular junction of the left coronary artery were formed by more smooth muscle cells and by a dense matrix of collagen type-I fibers, and d) the aortic sinuses and coronary arteries in structural ischemic heart disease specimens displayed structural alterations that affected the aortic tunica media and the collagen distribution at the sinotubular junction. CONCLUSIONS The morphological and structural differences observed between right and left sides suggest that the left aortic sinus is more resistant to traction and is, therefore, less prone to iatrogenic dissection. Structural ischemic heart disease is a risk factor that increases the likelihood of aortocoronary dissection.