In a method and apparatus for controlling transmission of wireless energy to a medical device (100) implanted in a mammal patient, the wireless energy is transmitted from an external energy source (104) located outside a patient and is received by an internal energy receiver (102) located inside the patient, for directly or indirectly supplying received energy to the medical device. An ultrasonic feedback control signal (S) is transmitted from an internal ultrasonic signal transmitter (110) located inside the patient to an external ultrasonic signal receiver (112) located outside the patient. The feedback control signal relates to the energy for operating the medical device and is used for controlling the transmission of wireless energy from the external energy source.
