Angiotensin converting enzyme (ACE) inhibitors have a myocardial protective effect, especially against the ischemia/reperfusion injury induced during coronary artery bypass grafting (CABG). Indications, dose, suitable time, and duration of administration, however, are still controversial. The heart that has undergone CABG has many pathological features, such as infarction-associated hypertrophy, myocardial stunning, vulnerability to arrhythmias, and coronary artery dysfunction. Recent studies indicate a significant role for ACE and angiotensin II receptor polymorphisms in the reaction to heart surgery. In this review, we discuss role of ACE in each pathological condition. Unlike conventional CABG, the newer off-pump CABG technique does not require cooling of the heart, and we discuss the temperature dependency of ACE inhibitors. The optimal use of ACE inhibitors in clinical practice requires consideration of many factors.