The antiocclusive effect of coronary dilatation with age.

Human coronary arteries were perfusion-fixed; sectioned and their external and lumenal circumferences measured by microscopic planimetry. They were found to dilate with increasing age, and this change seems to be more a degenerative process than a response to increasing heart weight. It is inferred that a moderate degree of coronary dilatation compensates for the tendency of atherosclerosis to occlude the lumen. Absence of any coronary dilatation might be hazardous in that the stenosing effects of atherosclerosis would be enhanced. By contrast over-dilatation (ectasia) is dangerous in that it causes a reduced flow-rate and, hence, promotes thrombosis.