On Friday, the 8th of October 1976, a one day Symposium on Cardiac Pacing, supported by an educational grant from Vitatron Medical, was held at the Sheraton Boston Hotel in Boston, Massachusetts. The intent of the Organizing Committee was to provide a concentrated overview of various aspects of cardiac pacemaker technology ranging from historical aspects, indications, electrode design, energy sources, engineering concepts, detection of malfunction and fol­ lowup of implanted systems. A look into future trends was also emphasized. The audience consisted of physicians from all parts of the United States with a special interest in pacemaker systems. Their comments, questions, and description of their own experiences, which arose during the discussion period at the end of the program, extended the breadth of the information provided. J . WARREN HARTHORNE ACKNOWLEDGEMENT The editors of this Colloquium on Cardiac Pacing (J. W. H. and H. J. Th. T. ) ac­ knowledge the patient understanding and support of their wives, Christa and lise through the long hours at night and weekends during which these proceedings were made ready for publication. A special note of appreciation is extended to Dr. Harthorne's secretary, Miss Stephanie Ann Murray, who transcribed the original tape-recorded presentations and typed and retyped the many corrected versions thereafter - all done without complaint and with ultimate good humor. CONTENTS Foreword . 5 J. WARREN HARTHORNE, M. D. Contributors . 9 Early History of Cardiac Pacing. II HILBERT J. TH. THALEN, M. D.