Sudden cardiac death (SCD) occurs in patients with Bartter/Gitelman syndromes. Hypokalemia and QTc prolongation are suggested mechanisms. SCD, however, has also been described at normal potassium concentration. This study reports the cases of one Bartter and one Gitelman patient, who experienced an aborted SCD, and evaluates the possible mechanisms of life-threatening arrhythmias and sudden death in these patients in order to contribute to a systematic screening/treatment protocol for them. After the episode of aborted SCD the patients underwent echocardiographic analysis at resting and during isometric exercise, complete electrophysiologic study and coronary angiography. Ventricular arrhythmias were not inducible during the electrophysiologic study, and coronary vessels were normal at angiography. Exercise induced LV dysfunction with reduction of cardiac index, paradoxical QTc prolongation and prolongation of QTc during nocturnal vagal stimulation in addition to hypokalemia might be identified as possible additional triggering factors for aborted SCD in these patients, leading to the conclusion that hypokalemia might not be the only factor capable of precipitating SCD in Bartter's/Gitelman's syndromes. The identification and recognition of other possible triggering mechanisms is extremely important in these patients and suggests the need for a systematic cardiac screening/treatment protocol for an effective prevention.