Abstract
Late histological changes occurring in aortocoronary bypass vein grafts were studied by light and electron microscopy in three dogs killed one, two and three years after grafting. The changes consisted of intimal thickening due to a proliferation of modified smooth muscle cells (myointimal hyperplasia) and replacement of most of the medial smooth muscle by fibrocytes. Serial angiography in the dogs did not reveal progression of the intimal thickening after one month.