Phrenic nerve injury has been reported with the use of iced slush for topical cardiac hypothermia. A review of the preoperative and the postoperative chest roentgenograms was performed to detect phrenic nerve injury in patients undergoing cardiac operation with the use of iced slush for topical hypothermia from January, 1985 to June, 1987. The reviewed series included 45 patients who had undergone valve replacement. In this review, the injured site of phrenic nerve was left in 13 cases, right in 1 case and the overall incidence of phrenic nerve paralysis following open heart surgery was 31%. Compared to the incidence of phrenic nerve paralysis in the control group [without pericardial insulation] [406, 12 cases/30 cases], that in the group of patients receiving pericardial insulation [13.3%, 2 cases/15 cases] was lower, but there was no statistical significance. The initial time that diaphragmatic paralysis developed was mean 3.5 days [range 1-8 days] postoperatively and the recovery time of the paralysis was mean 4.7 months [range 0.5-10.5 months] postoperatively.