Abstract-Geometric remodeling in de novo atherosclerosis and in restenosis after balloon angioplasty constitutes a change in total arterial circumference that, together with plaque growth or neointima formation, determines the lumen of the artery. The heterogeneous nature of arterial obstructions raises the question of whether early and late outcomes (restenosis) of angioplasty are affected by the degree and direction of de novo atherosclerotic remodeling. This study was designed to assess the relationship between atherosclerotic remodeling and the degree and mechanism of restenosis after balloon angioplasty. Atherosclerosis was induced in 27 peripheral arteries of 18 Yucatan micropigs by a combination of denudation and atherogenic diet. Balloon angioplasty was performed, with serial intravascular ultrasound and quantitative angiography before and after intervention and at 42 days' follow-up. We used the relative media-bounded area (MBA), defined as the MBA of the treated site divided by the MBA of the reference, before angioplasty as a measure of remodeling in de novo atherosclerosis and late MBA loss as a measure of remodeling after balloon angioplasty. Relative MBA before angioplasty was not correlated with angiographic and echographic acute gain after balloon angioplasty (rϭ. Key Words: remodeling Ⅲ intravascular ultrasound Ⅲ balloon angioplasty Ⅲ atherosclerosis Ⅲ restenosis G eometric remodeling in de novo atherosclerosis 1-4 and in restenosis after balloon angioplasty 5-9 constitutes a change in total arterial circumference that, together with plaque growth or neointima formation, determines the lumen of the artery. The change in total arterial circumference ranges from enlargement, which may lead to an actual increase in lumen size, to shrinkage. In the latter case, remodeling contributes to luminal (re)narrowing. The different contributions of remodeling and plaque formation to the atherosclerotic process result in a heterogeneity of atherosclerotic arterial obstructions, with a large plaque mass accommodated by a locally enlarged artery at one extreme and a small plaque in a focally shrunken artery at the other. The heterogeneous nature of arterial obstructions with respect to remodeling raises the question of whether early and late outcomes (restenosis) of angioplasty are affected by the degree and direction of de novo atherosclerotic remodeling and whether, for instance, a lesion based predominantly on shrinkage will restenose by remodeling rather than by neointima formation.In a recent serial IVUS study from our laboratory in human femoral arteries, 10 we observed no difference in acute lumen gain between three categories of de novo atherosclerotic remodeling, ie, enlarged, unchanged, and shrunken arteries. However, the mechanism of acute gain by balloon angioplasty was different, showing more plaque reduction or axial redistribution of plaque in enlarged arteries and more stretch of the arterial wall (increase in MBA) in shrunken arteries.Restenosis is the arithmetic sum of neointima formation, [11...