A heart monitor is disclosed including an electroacoustic transducer such as an earphone coupled to a controller. The transducer is positioned in a person's ear in acoustic communication with the tympanum. Signals from the transducer are processed to determine the presence of pulsatile blood flow. The heart monitor may be incorporated into a portable media playback device alternating between playback and monitoring mode or performing both simultaneously using one earphone for each function. The heart monitor may be incorporated into a defibrillator to sense the presence of blood flow for use in a shock delivery decision.