A well-conditioned 35-year-old athlete’s heart rate may increase only to 140 beats per minute during 12 minutes of such exercise. On resting, the heart rate should fall quickly to under 100 per minute within one to four minutes and to less than 70 beats within two to three minutes. During the recovery phase the ECG continues to be recorded because abnormalities caused by ischemia may be detected at this stage such as ischemic changes, premature beats, and arrhythmias.
The electrocardiographic hallmark of exercise-induced myocardial ischemia is depression of the ST segment. A horizontal or down-sloping ST segment depression equal to or greater than 1 mm in two or more leads is diagnostic. If this electrocardiographic change is noted at low levels of exercise, for example, less than four minutes on the treadmill, or at slow heart rates like less than 120 beats per minute, severe obstructive coronary artery disease is usually present.
Diagnostic and prognostic variables during exercise or recovery include:
• ST segment depression > 1 mm, horizontal or down-sloping
• ST segment elevation in leads lacking Q waves
• Chest pain and angina, relieved immediately by cessation of the exercise (within one to two minutes or relief with nitroglycerin)

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