The purpose of this project is to continue the development and testing of rechargeable hermetically-sealed cardiac pacemakers. The rechargeable power source in this unit is a specially designed hermetically sealed, silver modified mercuric-oxide-zinc cell, not a nickel-cadmium cell. In a series of simulated biological tests, this cell has demonstrated the capacity for over 40 years of function with infrequent recharging (once every 18 months). Without recharging, the pacemaker will function for over 4 years. At the end of this rundown period, this pacemaker can be recharged. Replacement would not be needed, as it would be in conventional mercury-zinc or even long-lifed lithium powered pacemakers. Therefore, this pacemaker can function as a primary unit, with or without recharging, at the discretion of the patient or his physician. The fixed rate version of this pacer continues to pace dogs in complete heartblock over four years. Clinical testing began over three years ago. To date, ten patients have received fixed rate rechargeable pacemakers. There have been no pacemaker problems in any patients. We will be continuing to monitor the dogs and human patients during this study with a built-in telemetric monitoring system. This monitoring system presently is capable of directly measuring cell voltage and rate through the intact skin. Studies are under way which will enable us to remotely monitor additional parameters such as lead wire integrity, hermeticity and even component status. In addition, new designs for programmable pacemakers are being examined. These units would be virtually free from interference due to electromagnetic energy (EMI).