medical electronic apparatus, namely, implantable prosthetic devices for arrhythmia control, namely, pacemakers, implantable cardioverter defibrillators, and endocardial and myocardial electrodes for use therewith; medical monitorng instruments, namely, electrode pacemaker analyzers and E.C.G. simulators; resuscitative and therapeutic instruments, namely, defibrillators; implantable muscle stimulators and intra-muscular leads, both used in connection with cardiomyoplasty