The question of whether reductions in blood flow occur under resting conditions in viable nonischemic myocardium in patients with coronary artery disease has been debated for >3 decades. Some early measurements reported reductions in resting left ventricular flow that seemed difficult to attribute to admixture of scar tissue with normally perfused myocardium.1,2 Others failed to show differences between apparently normal individuals and coronary patients.3,4 Transient defects in resting 201Tl scans observed in the late 1970s supported the concept of relative hypoperfusion of viable nonischemic myocardium. They were “usually associated with severe coronary artery disease but normal or only mildly abnormal left ventricular wall motion”5 and often were less pronounced after bypass graft surgery.6 Article p 3289 After the initial demonstration of myocardial “stunning” in 1975,7 it was increasingly appreciated that regional contraction often remained depressed after transient ischemia despite restoration of normal flow. Although stunning could persist for several days, its contribution to chronic left ventricular dysfunction remained unsettled. In a 1985 perspective on randomized trials of coronary bypass surgery in chronic stable angina, Rahimtoola8 proposed the term “hibernating myocardium” to describe a situation in which “contractility and metabolism and ventricular function are reduced to match the reduced blood supply.” He contrasted this situation with stunned myocardium, in which flow was not reduced proportionately to function. In an earlier study, Diamond and colleagues9 had referred to hypocontractile myocardium showing improved contractile function after coronary bypass surgery as being “in a state of function ‘hibernation’” but did not address whether preoperative blood flow was reduced concomitantly. Some subsequent studies have also used the term “hibernation” without reference to blood flow, whereas others have postulated that reversibly hypocontractile myocardium represents chronic stunning. Interest in whether resting blood …