The effect of halothane on the performance of myocardium supplied by a narrowed coronary artery has been assessed in an attempt to examine the influence of halothane on hearts with non-occlusive coronary artery disease. The study was divided into two parts: first, the left anterior descending (LAD) coronary artery was constricted beyond its second diagonal branch and, second, the left circumflex (LC) was constricted close to its origin In both parts, the myocardium was exposed to stepwise increases in inspired halothane before and after critical constriction of the vessel under study. Deepening halothane anaesthesia led to a dose-dependent depression of regional and global myocardial performance before critical constriction. After constriction, ischaemic changes in the contraction pattern of myocardium with a limited blood supply were noted If the ischaemia was confined to a small area of the heart (LAD stenosis) there was no significant deterioration of global LV performance. However, widespread ishchaemia (LC stenosis) led to irreversible heart failure in four of the five animals studied.