Calcitonin gene-related peptide (CGRP), a potent vasodilator released from capsaicin-sensitive C-fiber and A-fiber sensory nerves has been suggested to play a beneficial role in myocardial ischemia/reperfusion (I/R) injury. Because most previous studies showing a cardioprotective role of CGRP employed pharmacological experiments, the purpose of this study was to utilize a genetic approach by using mice with a targeted deletion of the -CGRP gene to determine whether this neuropeptide had a modulatory function on the severity of I/R injury. To accomplish this goal, isolated-perfused hearts from -CGRP knockout (KO) and wild-type (WT) mice were subjected to 30 minutes of ischemia followed by 5, 15, and 30 minutes of reperfusion. Cardiac functional parameters including coronary flow rates, left ventricular developed pressure (LVDP), maximum rates of pressure development (dP/dT), and left ventricular end diastolic pressure (LVDEP), were measured before and after I/R injury as were levels of creatine kinase (CK), to assess myocardial damage, and malondialdehyde (MDA), to assess oxidative stress. Following I/R injury, cardiac performance was significantly reduced in the hearts from the -CGRP KO mice compared to their WT counterparts. The marked reduction in myocardial function in the -CGRP KO hearts compared to WT hearts after I/R injury was associated with a significant elevation in CK release into the perfusates and MDA production in the cardiac tissue. Therefore, these data indicate that in this in vitro setting, deletion of -CGRP makes the heart more vulnerable to I/R injury possibly due, at least in part, to increased oxidative stress.