A device for recording and subsequently reproducing information, such as desired portions of an ECG signal produced by a heart prior to and during the occurrence of a disturbance in cardiac electrical activity. Two basic embodiments of the inventive recorder are contemplated. One embodiment is fully implantable and is encased with sensing and defibrillating electronics. With this embodiment, a low-power, low-capacity, continually updated recorder is continually operative, and a high-capacity stand-by recorder is actuated upon the sensing of fibrillation. An external device is used to retrieve by telemetry, the information stored in the implanted recorder. The second embodiment of the inventive recorder is an external device which has external electrodes for associating with the patient; ECG information is transmitted to the recorder unit by telemetry. Here, because power consumption is not so critical as with the implantable embodiment, a delay-type continually updated memory is continuously operative. Then, when any one of several types of arrhythmias is sensed, or when a defibrillating pulse is delivered, the data in the memory is "permanently" recorded on magnetic tape. Either embodiment may be used with an implantable defibrillator to record and subsequently reproduce information relating to the operation of the implantable defibrillator. The second embodiment also has an alarm capability to warn the patient should there be an interruption in telemetric transmission.