Necropsy and intravascular ultrasound (IVUS) studies in vivo show that while the angiogram is good at detecting high grade stenosis it is very insensitive for demonstrating the actual extent of atherosclerosis. Segments of an angiographically normal coronary artery can harbour many occult plaques.1 There are two reasons for this insensitivity. The first is that behind the plaque itself the media may vanish allowing the plaque to bulge into the adventitia rather than toward the lumen.2 In extreme cases the internal elastic lamina breaks allowing the plaque to be extruded from the artery wall. The second process is that of arterial remodelling (compensatory dilatation) described by Glagov.3 In this process when a plaque develops the arterial media remodels to allow the vessel to increase its cross sectional area and thereby accommodate the plaque without any reduction in lumen area. At the site of a plaque the vessel cross sectional area can be increased by anything up to twice that found at an adjacent reference segment of normal artery. What is interesting, and not well understood, is that the degree of remodelling varies widely from plaque to plaque. Within one coronary artery there may be a plaque with no remodelling, while in another segment of the same artery at the site of a plaque there may be a 100% increase in the artery cross …