Clinical signs and symptoms are extremely important in both suspicion and diagnosis of myocardial infarction (MI). The type of pain, its distribution, and its response to nitroglycerin may be very characteristic. However, it may not be easy to differentiate the pain of angina from that of acute infarct; in addition, 20%-30% (literature range, 1%-60%) of acute MIs have been reported to occur without chest pain. This is said to be more frequent in diabetics. Even when diagnosis is virtually certain on clinical grounds alone, the physician often will want laboratory confirmation, and this becomes more important when symptoms are atypical or minimal.