Schematic representation of a mouse heart, area of vasculopathy and explanation of the neointimal index and its limitations. A. Model of mouse heart with coronaries targeted for histologic analysis in dark grey. Because of their small size and variation in origin and path, there is a real possibility of failing to capture the area in histologic sections (lines) or missing true cross sections. B. An oblique cut through a vessel increases the apparent neointimal thickness in the linear dimension. C. For straight vessels, if the internal elastic lamina and residual lumens are approximately elliptical, the calculated neointimal index should give comparable results independent of the cutting angle of the vessels. D. For curved vessels, tangential sectioning close to the vessel wall will cause a falsely elevated neointimal index.