A device for the in vivo determination of the blood flow rate in a patients blood vessel includes a microelectrode arrangement provided for placement in the blood vessel, an electrical power source which provides excitation energy having physiologically harmless parameters for obtaining a measured signal, a signal detector for detecting an electrical measured signal resulting from the blood flow in the presence of the excitation energy at measuring electrodes of the microelectrode arrangement, and a signal evaluation device, connected to the signal detector, for determining the blood flow rate on the basis of the measured signal.
