Calcium has diverse roles in neuromuscular mechanisms. Within the cardiovascular system, hypocalcaemia is known to both impair myocardial contractility and prolong the QT interval, predisposing to ventricular arrhythmias. We present a case of chronic hypocalcaemia with prolonged QT interval associated with an atrial arrhythmia. Recent studies of congenital long QT syndrome suggest there is also a predisposition to atrial arrhythmias. Our case raises the hypothesis that acquired causes of long QT cause similar repolarisation abnormalities that predispose to atrial arrhythmias.