The present invention relates to an implantable battery-operated electrostimulation device (10), particularly for stimulating a heart, having a telemetry unit (11) for wireless data transmission between the electrostimulation device (10) and an external device (21), a control unit (15), which is connected to the telemetry unit (11) and is implemented to trigger a telemetric data transmission, a battery (13) for the power supply of the electrical components of the implant, such as the telemetry unit and the control unit, and a self-test unit, which is implemented to register the functional state of the electrostimulation device and independently detect acute or imminent malfunctions, the self-test unit (17) being connected to the control unit and the control unit being implemented to trigger a data transmission using data on the functional state of the electrostimulation device if an acute or imminent malfunction is detected.