The clinical course of two patients with congenital heart block who had pacemaker implantation at age 7 and 8 months, respectively, is reviewed. One patient at age 10 years has had nine pulse generators inserted; the other has had six implantations, the most recent a lithium iodine pacemaker, during 8 1/2 years of observation. Both patients have shown normal physical development and emotional maturation despite multiple hospitalizations and pacemaker replacements, thus demonstrating that electrical pacing, initiated in infancy, can be maintained through childhood without adverse effects.