Angina pectoris is a common disabling disorder and a clinical syndrome, caused by myocardial ischemia; an imbalance between myocardial oxygen supply and myocardial oxygen consumption. Thus, ischemia produces a typical series of events such as metabolic and biochemical alterations which lead to impaired ventricular relaxation and diastolic dysfunction, impaired systolic function, and electrocardiographic abnormalities and painful symptoms of angina. Transmembrane ionic currents are responsible for the cardiac potentials that are recorded as the electrocardiogram (ECG). The electrocardiographic profile of patients with angina pectoris is variate. The electrocardiogram provides critical information for both diagnosis and prognosis, particularly when a tracing is obtained during the episodes of pain. A completely normal electrocardiogram does not exclude the possibility of acute coronary syndrome. Serial ECG tracings improve the clinician's ability to diagnose acute and chronic coronary syndromes. The ECG may assist in clarifying the differential diagnosis if taken in the presence of pain. The resting ECG also has an important role in risk stratification. Exercise ECG is more sensitive and specific than the resting ECG as far as myocardial ischemia detection is concerned, and it represents the test of choice which helps identifying inducible ischemia in the majority of patients suspected of stable angina.