The complex ECG waveform the P-QRS-T-U waveform is a reflection of electrical events occurring in the heart during each contraction. Its interpretation requires an understanding of the ionic bases responsible for both the cardiac resting membrane potential and the cardiac action potential. Different ECG abnormalities occurring throughout the heart conduction system and muscle are reflected on the ECG. They are common and increase exponentially with age. They have the potential to alter the management of anesthesia. A substantial proportion of all deaths in most series of noncardiac operations result from cardiovascular complications. Thus, one would be justified in obtaining a screening ECG for symptomatic and asymptomatic patients suspected to have cardiovascular diseases. Advanced tests using ECG have been developed to detect suspected abnormalities e.g. Holter monitoring, and ECG stress test.