Background: Although the plaque ruptures leading to STEMI are known to cluster in the proximal one third of the left coronary arteries, the relationship between the spatial location of plaques and biomechanical properties of the normal looking left coronary artery is not determined. Therefore, we investigated the longitudinal distribution of plaques, endothelial dysfunction and distensibility in the angiographically normal LAD. Methods: In 28,249 cross sections of 134 patients without overt coronary artery disease and any medications (61.2짹11.2 yrs, 75 men), plaque (intimal thickness ��� 0.5 mm) areas were measured at 1-mm intervals using an automatic pullback device. The distensibility and vasoconstriction in response to acetylcholine (Ach) were measured in the proximal, mid and distal segments respectively. Results: The plaques were predominantly located in the proximal one-third of LAD (6-37mm: 82.4%) (Figure). As it was measured more distally, there was a constant decrease of the plaque burden in contrary to increasing the vascular response to Ach and distensibility in LAD (Figure). There was a significant reduction of distensibility in areas adjacent to the bifurcation points (Figure). Conclusions: The plaques were skewed towards proximal one-third of LAD. The existence of plaques per se was related to vascular distensibility, but not endothelial dysfunction in the normal looking LAD, suggesting a possible mechanism by which the reduced distensibility may be linked to plaque predilection for proximal segment.