Background: Cardioplegia is crucial for protecting the heart. Long-term cardiac protection is offered by the Del Nido Cardioplegia solution (dNCS). Aim: To compare conventional crystalloid cardioplegia with modified del Nido cardioplegia in mitral valve regurgitation replacement surgery. Objectives and Methods: This randomized clinical study included 80 patients undergoing to elective mitral regurgitation replacement surgery of both sex and age from 21 to 60 years with ASA (III and IV). All 80 patients were randomly assigned to receive conventional cardioplegia (St. Thomas’ cardioplegic solutions) or to obtain a modified del Nido cardioplegia (using normal saline) (groups A and B, respectively). The laboratory data for assessment of myocardial protection were obtained through measurements of preoperative serum levels of cardiac enzymes as, CK-MB, troponin, and lactate, immediately after operation, 12 and 24 hours postoperatively. Results: There was a significant increase in CK-MB only after 1 h (p < .001) in group (A) and after 12 h. CK-MB and lactate levels were significantly increased (p < 0.05). Also, after 24 h. CK-MB and Troponin T levels were significantly increased (p < .001). Regarding complications, one patient had atrial fibrillation and one case had permanent stroke in group (A), and two patients died in group (A), while one patient died in group (B) without a significant difference between the groups. Conclusions: We report that Modified Del Nido Cardioplegia has better postoperative chemical parameters as CK-MB, Troponin T and Lactate in mitral valve surgery in adults. DNC is a safe alternative to conventional cardioplegia and has achieved at least the same results.