This ECG is from a 31 year old female who had chronic renal failure. Her serum calcium level was decreased to 7.1 mg/dl. The QT interval is prolonged, measuring 0.48 seconds (480ms). This is due entirely to the lengthening of the ST segment which, in turn, is a reflection of the lowered serum calcium concentration. The P wave, PR interval, QRS complex and T wave are each normal. Sometimes, T wave changes may be associated with hypocalcemia. This occurs if the prolongation of the action potential plateau is not of equal magnitude throughout the myocardium. As a result, the sequence of repolarization will be altered and T wave morphology will be changed.