Coronary vasomotor tone: a heterogeneous entity.

Changes in coronary vasomotor tone are undoubtedly involved in the pathogenesis of many ischaemic coronary syndromes. The term coronary artery 'spasm' should be limited to the situations characterized by focal coronary constriction sufficient to cause transient total or sub-total coronary occlusion. Mild coronary artery constriction is also observed in many other situations, without even causing coronary artery occlusion. We present suggestive evidence that the mechanisms underlying coronary artery 'spasm' and 'physiological' coronary artery constriction are different.