['We studied the effects of diabetes on ventricular repolarization parameters and sudden cardiac death in patients with dilated cardiomyopathy (DCM).', 'We enrolled 132 consecutive patients in New York Heart Association (NYHA) heart failure functional classes II or III and left ventricular ejection fraction <40% without evidence of coronary artery disease. In 45 patients (34%), diabetes was diagnosed according to standard criteria (study group), and the remaining 87 (66%) had no diabetes (controls). All patients underwent a 5-minute high-resolution electrocardiogram recording for determination of QT variability (QTV) index and were followed for 1 year thereafter.', 'At baseline, the two groups did not differ in age, gender, left ventricular ejection fraction, NYHA functional class, or plasma brain natriuretic peptide levels. Similarly, QTV index did not differ between the study group (-0.51 +/- 0.55) and controls (-0.48 +/- 0.51; P = 0.48). During follow-up, 18 patients (14%) died of cardiac causes. Of the 18 deaths, eight were attributed to heart failure, and 10 to sudden cardiac death. Mortality was higher in the study group (10/45, 20%) than in controls (8/87, 10%) (P = 0.03). The same was true of the heart failure mortality (6/45 [13%] vs 2/87 [2%], P = 0.01), but not of the sudden cardiac death rate (3/45 [7%] vs 7/87 [8%], P = 0.78). By multiple variable analyses, diabetes predicted total and heart failure mortality, and a high QTV predicted sudden cardiac death.'] Does diabetes affect ventricular repolarization and sudden cardiac death risk in patients with dilated cardiomyopathy?