An implantable heart monitoring system has a control circuit that operates an implanted vibrator to emit a vibration signal that interacts with tissue in vivo. A vibration sensor detects vibrations after interaction with the tissue, and supplies a detection signal to the control circuit. The control circuit analyzes the vibrations in the detected signal relative to the vibration signal, and derives information concerning at least one mechanical property of the heart therefrom, such as stiffness and/or thickness of at least a part of the heart.
