Perioperative cardiac dysrhythmias cause significant morbidity and mortality. Their management requires thorough understanding and knowledge of distinctive molecular target to control cardiac excitability. The cause for cardiac dysrhythmias may be either disorders of impulse formation or disorders of impulse conduction, or both. Various factors leading to this during perioperative period may be hypoxia, hypovolemia, acid and electrolyte imbalance, hypoglycemia, hypothermia, pain, inadequate depth of anesthesia, placement of central venous lines, pulmonary artery catheter and chest tube, myocardial ischemia, cardiac tamponade, and tension pneumothorax. This chapter covers the ECG assessment to identify an unknown dysrhythmia, ECG components, identification of important dysrhythmias, supraventricular rhythms, conduction defects, and ventricular dysrhythmias.