A device and method is disclosed for improving tachyarrhythmia detection when the ventricles are resynchronized by delivering paces to both ventricles separated by a specified negative offset interval. Timing of escape intervals and tachyarrhythmia detection is based upon senses from one of the ventricles designated as a rate ventricle. Techniques are presented for preventing tachyarrhythmia detection from being compromised when the rate ventricle is paced after the other ventricle.