Objective     To analyze the effect of myocardial protection between modified Del Nido cardioplegia and St. Thomas Hospital Cardioplegia in adult patients with aortic valve and mitral valve replacement. Methods     From January 2014 to June 2016, 140 patients underwent aortic valve and mitral valve replacement in our hospital. According to different cardioplegia, the patients were divided into two groups including a modified Del Nido cardioplegia group (70 patients, 37 males, 33 females at mean age of 53.13±9.52 years) and a St. Thomas cardioplegia group (70 patients, 32 males, 38 females, at age of 50.71±9.29 years). We collected clinical data of the patients before operation (T1), 2 h after aortic unclamping (T2), 24 h after operation (T3) and 48 h after operation (T4). Indexes of muscle enzymes including blood center creatine kinase (CK), creatine kinase isoenzyme (CK-MB) concentration and liver function indexes including urea nitrogen (BUN), creatinine (Cr), alanine aminotransferase (ALT), aspartate aminotransferase (AST) concentrations, and compared the postoperative and follow-up clinical data. Results     There was no statistical difference in age, weight, gender, ejection fraction baseline data between the two groups (P>0.05). All patients were successfully completed  combined valve replacement under cardiopulmonary bypass. The cardiopulmonary time was no statistical difference between the two groups (P>0.05). However, compared with St. Thomas cardioplegia group, modified Del Nido group was less in perfusion (1.19±0.39 vs. 2.99±0.75, P<0.001), shorter in aortic clamping time (P=0.003). No statistical difference was found in defibrillation rate after resuscitation between the two groups (P=0.779). Biochemical indicators were not statistically different at different time points between the two groups (P>0.05). Conclusion     Modified Del Nido cardioplegia has the same effect on myocardial protection with St. Thomas cardioplegia in adult patients. It reduces the frequency of reperfusion, and shortens the clamping time. There is no additional injury in the important organs such as liver, kidney. Modified Del Nido cardioplegia myocardial protection ability in adult heart valve surgery is feasible.