A heart attack is a serious complication of bypass surgery. Heart attacks can occur in 4 out of 1,000 procedures. During stressful events, such as open heart surgery, your heart requires more blood and oxygen to function properly. If a certain artery or vessel is narrowed or blocked, it cannot send enough blood and oxygen to meet the demands of the heart muscle. Lack of oxygen can damage the heart muscle. Sometimes this lack of oxygen is only temporary, a condition called ischemia. However, if the section of heart muscle goes too long without enough oxygen, permanent damage can occur, and the area of the heart muscle can die. This is what occurs during a heart attack.