GP531 is a potent, second-generation adenosine regulating agent, is pharmacologically silent under basal conditions but increases localized endogenous adenosine during ischemia. IC50 & Target: Adenosine Receptor^[1] In Vivo: Low-dose GP531 reduces infarct size by 34% compared with vehicle and reduces the extent of the anatomic no-reflow zone by 31% compared with vehicle. Infarct size and zone of no-reflow in the high dose are reduced by 22% and 16%, respectively. GP531 does not affect hemodynamics or blood flow. GP531 is effective at the lower dose in reducing the severity of ischemic/reperfusion injury, without inducing the adverse hemodynamic effects associated with adenosine administration such as bradycardia and hypotension^[1]. GP531 infusion has no effect on heart rate or mean aortic pressure but significantly decreases left ventricular end-diastolic pressure, end-diastolic volume, end-systolic volume and end-diastolic wall stress. GP531 significantly increases left ventricular EF, deceleration time of early mitral inflow velocity and the slope of end-systolic PVR without increasing MVO2^[2].