Introduction & Objective: The role of free radicals in reperfusion injury has been revealed in the previous studies. Protective effects of endogenic antioxidants include glutathione has been shown in cardiomyocyte. Intracellular L-cysteine availability is one of the major rate limiting factors in glutathione production. This study aimed to investigate the role of L-cysteine in the preservation of cardiac function after cardioplegia in the isolated rat heart.

Materials & Methods: For this purpose Wistar male rat in two control (n=10) and test (n=6) groups were used. Hearts were isolated according to working heart method and perfused by Kreb’s solution. Different cardiac parameters include aortic pressure and flow, left atrial pressure and coronary solution flow were recorded during the experiment. Experimental protocol for each heart composed of three following stages: First, basal stage for stabilization of cardiac function (25min), second, cardioplegia (25min), finally, reperfusion (30min). L-cysteine (5mmol/lit) was added to the solution in the test group for 10min before and after cardioplegia. Unpaired t-test and ANOVA were used to analysis and comparison between control and test groups.

Results: The results showed that the recovery percentage of aortic pressure and flow after cardioplegia in test group were 91.2 ± 1.69  (%) and 61.176± 3.98 (%) respectively, and they were significantly higher than those of control (85.74± 1.28 and 44.495± 4.85 (%) , p= 0.0213 and p= 0.0324 respectively).

Conclusion: Therefore these results indicate the better cardiac function after cardioplegia in cysteine group in comparison to control that is probably due to antioxidative effect of cysteine. With regard to importance of cardioprotection, complementary experiment for elucidation of cellular mechanisms of this effect and its clinical usage are suggested.