Objective:To study the myocardial protective effects of exogenous supplement of nicotinamide adenine dinucleotide (NAD) in cardioplegic solution on rats undergoing extracorporeal circulation.Methods:Twenty-four SD rats were randomly divided into sham, model, and NAD 50, 200 mg/L groups, with 6 rats in each group, according to the random number table method. The rats in the sham group were only anesthetized and tracheally intubated, connected to a ventilator for respiratory support, and the extracorporeal circulation model was not established. Except the sham group, the model of extracorporeal circulation in rats was established by blocking the ascending aorta. The model group was then perfused with cardioplegic solution without NAD; the NAD 50 mg/L group was perfused with cardioplegic solution containing 50 mg/L NAD; and the NAD 200 mg/L group was perfused with cardioplegic solution containing 200 mg/L NAD. After five minutes of cardiac arrest, the aortic cross-clamp was removed to restore blood flow to the heart and allow the heart to gradually resume beating. Plasma and cardiac tissues were collected from each group of SD rats. The effects of NAD in cardioplegic solution on myocardial injury in the extracorporeal circulation model were examined by hematoxylin-eosin staining. The cross section area of cardiomyocytes was quantitatively analyzed by wheat germ agglutinin staining. The number of CD3-positive cells per unit cross section area was determined by immunohistochemical method. Levels of the inflammatory factor tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were measured by enzyme-linked immunosorbent assay. The relative mRNA expression of cysteine aspartic acid specific protease-3 ( Caspase-3), B-cell lymphoma-2 ( Bcl-2), Bcl-2 associated X protein ( Bax) and superoxide dismutase-2 ( SOD-2) was determined by real-time fluorescence quantitative PCR. Results:Compared with the model group, the cross section area of cardiomyocytes [(422.54±2.36) μm 2 vs (450.53±32.04) μm 2], the number of CD3-positive cells per unit cross section area [(150.49±34.17) cells/mm 2 vs (220.54±35.23) cells/mm 2], the expression levels of TNF-α [(69.37±8.82) pg/ml vs (76.08±9.02) pg/ml] and IL-6 [(130.72±15.54) pg/ml vs (144.19±11.98) pg/ml] were decreased in the NAD 50 mg/L group, and the mRNA expression levels of Bcl-2 (0.59±0.03 vs 0.46±0.07) and SOD-2 (0.62±0.06 vs 0.48±0.07) were increased in the NAD 50 mg/L group, however, the differences were not statistically significant (all P>0.05). The relative mRNA expression levels of Caspase-3 and Bax in the NAD 50 mg/L group were lower in the model group (2.23±0.32 vs 2.96±0.26, 2.42±0.08 vs 3.04±0.06) ( P<0.05, 0.01). Compared with the model group, the cross section area of cardiomyocytes [(383.35±8.12) μm 2], the number of CD3-positive cells per unit cross section area [(101.23±3.77) cells/mm 2], the expression levels of TNF-α and IL-6 [(51.70±4.64) pg/ml and (102.25±9.42) pg/ml], and the relative mRNA expression levels of Caspase-3 and Bax (1.41±0.09 and 1.45±0.07) were decreased ( P<0.05, 0.01). The relative mRNA expression levels of Bcl-2 (0.81±0.01) and SOD-2 (0.78±0.03) were increased (all P<0.01). Conclusions:Exogenous supplement of NAD in cardioplegic solution can effectively reduce circulating inflammatory cytohines and inhibit myocardial tissue apoptosis and myocardial injury.