Atheromatous coronary artery disease progresses by atheroma accretion, plaque rupture and thrombus formation, with or without spontaneous fibrinolysis. The natural history may be altered by modifying risk factors in an attempt to induce regression, or treated by mechanical means such as balloon angioplasty, directional coronary atherectomy or drills, or flow modulated by the insertion of an aorto coronary bypass graft with or without endarterectomy. Here we discuss the natural history of the atheromatous disease in a series of 355 patients who underwent at least one PTCA procedure and then underwent a second angiographic study to determine the changes in the dilated and nondilated arteries.