It has been determined that certain dual-chambered cardiac stimulators may operate in a region in which an atrial pacing event may obscure the detection of a ventricular tachyarrhythmia. Various exemplary techniques may be used to improve the ability of dual-chamber cardiac stimulators to detect such ventricular events. In accordance with one technique, it is determined whether a ventricular event should be classified as a ventricular tachyarrhythmia. If not, the VA interval is restarted as usual. However, if the ventricular event may be classified as a ventricular tachyarrhythmia, it is determined whether the ventricular event falls within the region in which an atrial pacing event may obscure its detection. If not, then the VA interval is restarted as usual. However, if the ventricular event falls within this region, the VA interval is restarted with the VT rate detection boundary. This has the effect of lengthening the VA interval and the AA interval in this region so that atrial pacing events will not obscure the sensing and treatment of ventricular tachyarrhythmias in the region.