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After taking the history and physical, the physician will likely next undertake the classic electrocardiogram (EKG or ECG). Initially performed at rest, this test can also be performed in conjunction with exercise—the so-called exercise-tolerance test, or stress test. The EKG records the electrical activity of the heart through monitors placed on the skin. This electrical activity is recorded in waveforms that provide evidence of the timing between different chambers of the heart. By looking at the electrical pattern of the EKG, the physician can try to estimate the heart's appearance and function. For example, an EKG might reveal evidence of a previous heart attack, or enlargement and/or thickening of the heart due to high blood pressure or valvular diseases. If a patient has experienced a previous, undiagnosed heart attack, the physician can sometimes detect that event through a corresponding change in the EKG, the heart's electrical signature.
While the EKG provides some sensitivity, it lacks specificity. It offers a useful tool for an initial screening and can also help to put findings into an important context. However, additional tests are often required to confirm a diagnosis. An abnormal EKG really refers to any variation from the average tracing of a normal person. Some patients with healthy hearts always have an abnormal appearance to their EKG. Conversely, some patients with significant heart disease may still produce an apparently normal EKG reading, even while experiencing a heart attack. We should therefore rely on EKGs as just one of our mix of diagnostic tools.
 
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