Much controversy persists regarding the optimal techniques for myocardial protection during heart surgery. Numerous studies have compared warm cardioplegia with cold cardioplegia for myocardial preservation, but the outcomes were inconclusive. The aim of this meta-analysis of randomised controlled trials (RCTs) was to compare the beneficial and harmful effects of warm and cold cardioplegia during heart surgery. Electronic databases and manual bibliographical searches were conducted. A meta-analysis of all RCTs comparing warm cardioplegia to cold cardioplegia perfusion during cardiac surgery was performed. Data for clinical events (in-hospital death, myocardial infarction (MI), low output syndrome, postoperative use of intra-aortic balloon pump, stroke and atrial fibrillation), postoperative cardiac index, postoperative creatine kinase-MB (CK-MB) and cardiac troponin release were extracted, and we summarised the combined results of the data of the RCTs as relative risk (RR), with 95% confidence intervals. A total of 41 RCTs including 5879 patients were assessed in this study. We found that there was no statistical difference between patients receiving warm cardioplegia and cold cardioplegia in the incidences of clinical events. Warm cardioplegia was associated with improved postoperative cardiac index. CK-MB and cardiac troponin concentrations after surgery were significantly lower in the warm group as compared with the cold group. Using warm cardioplegia for myocardial protection during heart surgery resulted in similar incidences of clinical events, significant improvement in postoperative cardiac index and reduction in postoperative enzyme release as compared with cold cardioplegia. © 2009 European Association for Cardio-Thoracic Surgery.