An external defibrillator used to treat a patient wirelessly communicates with an implantable medical device (IMD) implanted in the patient. In some embodiments, a telemetry head may be removably coupled to the external defibrillator to facilitate communication with the IMD. The defibrillator may receive information, such as patient, device, physiological, and treatment information, from the IMD. The defibrillator may use some or all of this information during treatment of the patient. For example, the defibrillator may prompt a user, or modify programmed user prompts based on the information. The defibrillator may deliver therapy based on the information. The information may include real-time values of physiological parameters monitored by the IMD, which may be displayed by the external defibrillator. The external defibrillator may control delivery of therapy by the IMD. The defibrillator may collect medical event information during treatment of the patient, and store the medical event information in the IMD.