Two consecutive series of 47 myocardial pacemaker implantations and 265 transvenous implantations have been analyzed. Transvenous pacemaker implantation is now performed in all instances but those in which atrial synchronous pacing is used or in which the patient is young and growth is to be expected. The major problems are electrode perforation of the heart and short life of the pacemaker pulse generator. © 1969.