The etiology of congenital and acquired complete heart block is discussed. The prognosis is much better in mostly congenital suprabifurcational blocks, than in the infrabifurcational blocks, which are acquired in most instances. Suprabifurcational blocks are characterized by normal QRS complexes, higher heart rates, and adequate frequency adaptation to exercise. Widened and deformed QRS complexes and fixed heart rates as low as 40--50 beats per minute are typical in infrabifurcational blocks. Whereas children with congenital heart blocks only eventually need pacemakers, the immediate implantation of a pacemaker is mandatory in children with acquired heart blocks after a decrease of the heart rate below 30--40 beats per minute and/or after an Adams-Stokes attack. With demand pacemakers being available, fixed rate systems are obsolete for children. Lithium batteries should be preferred for their smallness and their larger life span. A considerable body of surgical and technical problems due to infection, wire damage, and other complications still awaits solution.