 Participants in this study will either have heart failure HF and are scheduled to undergo cardiac resynchronization therapy pacemaker CRT-P or cardiac resynchronization therapy defibrillator CRT-D implantation, or have atrioventricular AV block and are scheduled to undergo dual chamber pacemaker implantation. In this study additional heart rhythm measurements will be collected during the implant procedure to better understand how His bundle andor parahisian pacing HISP effects electrical conduction in the hearts of patients with HF or AV block. 