The proarrhythmic potential of therapeutic drugs can be evaluated by in-vivo electrophysiological testing using stimulated bradycardias. Since conventional stimulators are limited in the number of bradycardic beats, they cannot be used to evaluate the dynamic change of QTintervals from the onset of bradycardia until a steady state has been achieved. Therefore, we designed and implemented a computer-based programmable stimulator, that enables complex stimulation protocols. This application was then tested in an experimental guinea-pig model to evaluate the characteristics of droperidol-induced QT-interval prolongation.