Abstract: Methods and systems for dynamically modifying pacing timing and backup pacing delivery in cardiac stimulation devices include applying pacing impulses, measuring corresponding responses, and, based on such responses, automatically modifying timing or operational settings of the stimulation device to improve pacing functionality. Among other things, the approaches described herein reduce unnecessary backup pacing impulses in HIS bundle pacing applications, facilitate fusion in bundle branch block applications, and automatically enable or disable backup pacing in response to achieving QRS complex correction.