The coronary steal phenomenon (not to be confused with the "coronary steal syndrome" after IMA bypass and occlusion of the A.subclavia) is a drug-induced redistribution of blood flow through the coronary arteries, which is associated with a reduced perfusion of arteriosclerotic stenosed coronary vessels (CHD).
The autoregulation of coronary blood flow results in the dilatation of resistance vessels in the subendocardial myocardium. If drugs (e.g. Ca+channel blockers) widen the resistance vessels even in the well perfused myocardium, but the stenosed coronary vessels are not dilated, a steal phenomenon with redistribution of blood flow to the disadvantage of the subendocardial myocardium can occur. The consequence is a drop in perfusion pressure with ischemia in these myocardial sections.