ECG trace. Computer artwork of an ECG (electrocardiogram) trace from a healthy heart. An ECG uses electrodes to measure the electrical activity of the heart during the pumping of its chambers, and records it as an electrical wave (yellow). For example, the tall peak seen here represents the contraction of the heart's lower chambers (ventricles). Electrocardiography is a useful tool for the diagnosis of heart disease. The waves of an ECG trace can reveal the nature and location of many cardiac disorders.