Because of increasing myocardial damage by normothermic arrest, most of cardiac surgeons now uses many kinds of method reducing myocardial injury, such as systemic hypothermia, topical cooling and cold cardioplegic solutions. And phrenic nerve paralysis has been reported with the use of iced slush for topical cooling. So we reviewed the preoperative and postoperative chest X-rays of 54 patients undergoing open heart surgery with the use of iced slush for topical cooling to find phrenic nerve paralysis. Four of 54 patients were known to have phrenic nerve paralysis. The first time known to develop phrenic nerve paralysis was from POD 4 1 day to POD 4 3 day and the phrenic nerve paralysis resolved within a month postoperatively except one. A patient have had phrenic nerve paralysis persistently over 7 months. And the effect of unilateral phrenic nerve paralysis was of no clinical significance.