Devices, systems, and methods are disclosed for relaying information from a cardiac pacemaker to an external device. Logic on the pacemaker modulates a heartbeat clock of the pacemaker to encode information onto a blood pressure sequence by adding or subtracting a small subinterval to or from a pulse repetition interval of the pacemaker. A muscle stimulator beats the heart according to the modulated sequence. A monitoring device external to the body monitors the blood pressure to retrieve the encoded information, or message. The encoded information is then decoded to determine the information in the message. This information may concern the pacemaker as well as other devices within the body that communicate with the pacemaker such as blood monitors, etc. Since the message is conveyed via simple modulation of the heart beat intervals, no separate transmitter is required in the pacemaker which would otherwise increase cost and decrease battery life.