Objective To evaluate the effect of calcitonin gene-related peptide(CGRP) intravenous on myocardial injury and the oxygen free radicals in rats. Methods Rat myocardial injury model was established by subcutaneous injection of single dose isoproterenol(ISO), and then treated with CGRP single dose IV. Two hours after treatment, blood was taken for determining serum CK,LDH,MDA and SOD tests,and the myocardial tissue was homogeniged for determining tissue MDA and SOD, and microstructures observation proceeded. Results (1)When group ISO injury was compared with the group control, its serum MDA and tissue MDA levels increased apparently,but its serum SOD and tissue SOD levels decreased (P<0.05). Compared with that in group ISO injury the serum MDA and tissue MDA in CGRP treatment group decreased obviously, but its serum SOD and tissue SOD increased obviously(P<0.05). (2)Serum CK and LDH levels in group treatment decreased clearly as compared with that in group injury (P<0.05). (3) Microstructure observation showed that the injury degree of myocardial structure in group CGRP treatment was much less severe than that in group injuried(P<0.05). Conclusions The results suggest that CGRP has effects of protecting the myocardial injury induced by isoproterenol, correcting the imbalance between MDA and SOD level, inhibiting the stronger lipid hyperoxide reaction, preventing the myocardial enzyme leak from injuried cardiomyocyte and antagonizing arrhythmia in rats.