The pacing threshold is the minimum amount of stimulus energy that can sustainably capture the myocardium. The pacing threshold is dynamic in vivo. During the first 24 h of electrode lead implantation, changes in myocardial pacing threshold are minimal and may decrease slightly. Over the next 7 to 10 days, myocardial tissue in contact with the electrodes undergoes damage, necrosis, and fibrosis, and the pacing threshold increases dramatically. The peak of the pacing threshold generally occurs 2 weeks after electrode lead implantation and then decreases gradually, stabilizing after 3 months.