A biventricular pacing system is provided which includes an automatic capture verification system for verifying capture of left ventricular pacing pulses on a beat by beat basis. A loss of capture recovery system delivers a backup safety pulse in the event of loss of capture detected in either the right or left ventricle. An automatic stimulation threshold search system is provided for measuring the capture threshold of both left and right ventricles based on various triggers. An automatic output regulation system for both the left and right ventricular channels is provided to set the pacing amplitude to levels sufficient to ensure capture plus a safety margin. A left ventricular automatic stimulation threshold search is triggered upon detection of any loss of capture in the left ventricle and periodically based on a number of different triggers.