Intraoperative thermographic evaluation of regional myocardial cooling induced by cardioplegia, in patients with coronary artery disease, was conducted in 22 cases. Pictures were obtained at the beginning of the cardiopulmonary by-pass, after general cooling and during cardioplegic infusion. Uneven myocardial cooling was observed related to the degree of coronary artery stenosis. After the distal anastomosis of the saphenous vein by-pass graft was completed, injection of cold solution in to the graft showed marked cooling of the dependent myocardium, proving the patency of the graft. In the case of internal mammary artery graft (IMA), after the anastomosis was completed, releasing the bull-dog clamp on the IMA graft, allowed a flow of relatively warm (30 degrees C) blood in the anterolateral wall of the cold (20 degrees C) heart. A warm spot appeared in the thermographic pictures, assessing the patency of the IMA graft. Thermography appears to be a useful tool during myocardial revascularization in order to assess proper myocardial cooling during cardioplegia, and to check intraoperative patency of saphenous vein graft and IMA graft. The use of a special mirror prevents interference with the surgeon's work.