Tegaserod (HTF 919) is a new drug being developed for gastrointestinal motility disorders. Because other gastrointestinal prokinetic agents, such as cisapride and erythromycin, cause slowing of cardiac repolarization and have been implicated in the development of the potentially fatal ventricular arrhythmia, torsades de pointes, a study was initiated to determine whether tegaserod and its main human metabolite adversely influence cardiac repolarization. By using isolated Langendorff-perfused rabbit hearts, we show that QT intervals remain unchanged at concentrations of tegaserod from 0.5 to 10 microM. It was not until the tegaserod concentration was increased to 50 microM (roughly 500-5,000 times more concentrated than those typically found in human plasma after administration of recommended clinical dosages), that a small, but significant increase in the QT interval (12+/-4%; p < 0.05; n = 4) was observed. No significant changes in QT occurred in the presence of the tegaserod metabolite at any of the concentrations tested (0.5-50 microM). In contrast, cisapride caused QT lengthening at concentrations as low as 0.1 microM, with significant QT increases occurring when 5-50 microM cisapride was used (22+/-4% to >70%, respectively; p < 0.01; n = 4). Erythromycin also caused significant lengthening of QT intervals (11+/-2%; p < 0.001; n = 4), although 100 microM concentrations of this drug were required to achieve this effect. These results demonstrate that both cisapride and erythromycin can slow cardiac repolarization at therapeutic doses and that tegaserod's lack of QT prolongation at therapeutic doses suggests that it has the potential to be a safer alternative to cisapride as a gastrointestinal prokinetic agent.