Energy-wasteful total Ca2+ handling underlies increased O2 cost of contractility in canine stunned heart

Postischemic myocardial stunning halved left ventricular contractility [end-systolic maximum elastance (Emax)] and doubled the 02 cost of Emax in excised cross-circulated canine heart. We hypothesized that this increased 02 cost derived from energy-wasteful myocardial Ca(2+) handling consisting of a decreased internal Ca(2+) recirculation, some futile Ca(2+) cycling, and a depressed Ca(2+) recirculation fraction (RF) from the exponential decay component of postextrasystolic potentiation.