Few studies have reported re-sternotomy after an omental flap procedure. We describe the case of a 78-year-old man who received re-sternotomy after omental flap procedure for deep sternal wound infection and successfully underwent coronary artery bypass grafting. Although preoperative computed tomography showed funnel chest and limited space between the sternum and omentum, re-sternotomy was performed safely using circular electric sternum saw under partial cardiopulmonary bypass. Because the omentum functioned as cushioning material between the sternum and mediastinal organs, no injuries of the mediastinal organs occurred. An ultrasonic scalpel effectively dissected between the omentum and mediastinal organs, especially above the ascending aorta. The targeted coronary arteries were easily detected. The patient experienced no major cardiac or infectious events for three months. An ultrasonic scalpel is recommended for dissecting between the omentum and mediastinal organs.