It has been known that myocardial ischemia, a hypoxic condition induced by blood flow restriction, increases Ca2+ concentration in cardiomyocytes, and it is associated with abnormal cardiac function.13 Cardiac ADPR cyclase, a protein distinct from CD38 or the archetypical ADPR cyclase from A. californica, has not been cloned to date.39 To verify the direct relationships between higher level of cADPR and ischemic injury, the identification of cardiac ADPR cyclase is necessary. Here, CD38 is linked to myocardial ischemia.