Coronary arteries are, by definition, small vessels. When Grüntzig was about to move his balloon technique from the peripheral vessels to coronary arteries, people knew that it would never work. They knew that this was pushing the limits of the technique too far. The dissections, known to be germane to balloon angioplasty from looking at the postinterventional angiograms of leg arteries at the time, needed space not to obstruct flow and cause acute closures. People were wrong. The high flow in epicardial coronary arteries that further accelerates during diastole seems to make up for small size to a certain degree. Acute occlusions did occur more frequently in coronary than in femoral arteries but they still were confined to fewer than 10% of cases.

Nevertheless, a relation between the risk of acute closure and the diameter of the treated coronary artery became apparent. Small coronary arteries are not the friends of interventional cardiologists and very small ones are their nightmares.

The disadvantages of small coronary arteries are shown in table 1. The only advantage of small coronary vessels is that they generally subtend less myocardium, which translates into less clinical risk in case of an occlusion of the artery.