Abstract: A high speed telemetry system for implantable devices such as a pacemaker includes a transmitter disposed in an implantable housing and an external receiver. Typically the housing is metallic and it attenuates drastically electromagnetic signals having frequencies above a relatively low cut-off frequency. The transmitter includes circuitry for generating cosine waves of different frequencies and for selectively assembling these waves to define a set of data symbols. Preferably one of the frequency is a multiple of the other. Integer halve-periods of the waves are selected to define the symbols such that the overall data transmission rate exceeds the cutoff frequency. The external receiver synchronizes itself to the transmitter, and decodes the symbols using a constellation chart to decode the symbols into binary data.