Cardiac repolarization, represented on the ECG by the QT interval, is of particular clinical interest in critical care. Once it is measured and corrected for changes in heart rate, the QT interval is known as the QTc. Measurement of the QT interval is important because a prolonged QT interval is associated with ventricular tachycardia and sudden cardiac death. Despite the serious complications associated with a prolonged QT interval, the interval is not routinely measured because a standardized method for measuring it has not been established and the length of QT interval critical to the development of ventricular tachycardia has not been determined. Much has been written about the conditions associated with prolonged QT intervals and specific actions to take when complications appear. Guidelines to be used for QT analysis in the clinical area, based on currently available information, include (1) procedures for measuring QT interval and calculating QTc, (2) procedures for QT analysis, (3) warning signs that indicate increased risk of ventricular tachycardia associated with a prolonged QT interval, and (4) actions to consider once increased risk is determined.