The ECG is an indispensable tool in the ICU for the detection and diagnosis of heart disease. ECG abnormalities however can be present in a wide variety of noncardiac conditions, complicating the differential diagnosis with primary cardiac pathology. This overview discusses the ECG abnormalities and their pathophysiologic basis in the most frequently encountered noncardiac conditions, such as electrolyte abnormalities, pulmonary embolism, CNS diseases, esophageal disorders, hypothermia, and drug-related and other conditions. Knowledge of the characteristic ECG changes may provide early clues to the presence of these disorders, the prompt recognition of which can be life saving.