Telemetry apparatus for implantable tissue stimulator

An improved telemetry system for telemetering digital data from an implantable tissue stimulator such as a heart pacemaker (11). A carrier signal is pulse modulated in accordance with either or both of stored digital data and a digitized electrocardiogram signal, for coupling onto an electrical lead (13, 15) connected directly to the heart (17). This arrangement facilitates the transmission of substantially higher data rates than previously could be achieved.