Background- In a prospective, randomized trial, we compared intermittent antegrade tepid blood (TB) with cold crystalloid (CC) cardioplegia in patients undergoing coronary artery bypass grafting (CABG). Methods- One hundred thirty-seven consecutive patients who were candidates for CABG were randomized into two groups. Group I (n=65) received TB cardioplegia and group II (n=72) received CC cardioplegia. In both groups during surgery, the body temperature was maintained between 28-30^0C. Interval of delivery of tepid blood and cold crystalloid cardioplegia was less than 20 and 20 - 25 minutes, respectively. Results- The number of grafts, duration of cardiopulmonary bypass and total aortic cross clamp time in both groups were similar. Sustained electromechanical cardiac arrest failed to occur in 8% of the patients with TB cardioplegia. After reperfusion, spontaneous return to sinus rhythm was higher (P<0.02) and need for inotropic drugs was lower (P<0.0001) in TB group than in CC group. In the intensive care unit, creatine kinase-MB fraction was higher in the CC group. On the sixth day of operation, pericardial effusion by transthoracic echocardiography was lower in the TB group than in the CC group (P<0.0001). Conclusion- Intermittent antegrade tepid blood cardioplegia is clinically reliable and could be used safely for protection of the myocardium (Iranian Heart Journal 2002, 2003; 3(4&4( 6-11).