The aim of this randomized control trial, repeated-measure design was to investigate the effects of cold therapy in reducing pain after cardiac surgery during the first 72 postoperative hours. Seventy participants were matched and were randomly assigned to the intervention (n=35) or control group (n=35). The experimental group received a sterile cold gel pack to maintain the skin temperature at 10-15 °C for 20 min. The control group received the routine care. Acute pain was measured using a Thai version of the modified Brief Pain Inventory. The data were analyzed with repeated measures MANOVA. The results showed that the experimental group had significantly lower mean pain than the control group (P<0.001). In addition, pain scores in the experimental group were significantly decreased during the first 72 postoperative hours (P<0.001). Thus, the cold therapy was effective in reducing pain after cardiac surgery during the acute phase.