The purposes of this study are to evaluate the clinical usefulness of maximum QTc and QTc dispersion determination in aortic stenosis, and to compare the effects of maximum QTc and QTc dispersion on the risk of syncope in aortic stenosis. The QT interval dispersion has long been known to be a marker of dispersion of ventricular repolarization and, hence, electrical instability. Additionally, it has been shown that these patients have a propensity to ventricular tachyarrhythmic syncope. The study included 86 patients with aortic stenosis who underwent left-heart catheterization and coronary angiography during investigation of syncope and 30 healthy subjects. The patients were characterized with regard to the presence or absence of a history of syncope and the severity of aortic stenosis (the degree of peak transvalvular gradient). In addition, QT max and QT dispersion measurements were corrected for heart rate according to Bazett's formula. The QTc max and QTc dispersion were greater in patients with aortic stenosis than in the healthy subjects (477 +/- 49 ms vs 370 +/- 22 ms, p<0.001; 60 +/- 13 ms vs 38 +/- 1 ms, p < 0.001). Similarly, the QTc max and QTc dispersion were greater in the patients with a history of syncope than in the patients with no history of syncope (493 +/- 48 ms vs 459 +/- 4 ms, p < 0.001; 68 +/- 12 ms vs 53 +/- 10 ms, p < 0.001). In addition, both parameters were greater in the patients with a high transvalvular gradient than in the patients with a low transvalvular gradient (489 +/- 49 ms vs 451 +/- 39 ms, p < 0.001; 65 +/- 12 ms vs 50 +/- 9 ms, p < 0.001). Multivariate logistic regression analysis showed that only a increased QTc dispersion had significant value for the risk of syncope in aortic stenosis. An increased QTc dispersion caused a 10.4% increase in the occurrence of syncope in aortic stenosis. These results suggest that high values of QTc dispersion are sensitive noninvasive markers to determine the risk for syncope in aortic stenosis.