The present invention relates to an eavesdropping device for monitoring measured physiological variables of an individual, which eavesdropping device comprises a receiver and a communication interface. The eavesdropping device of the present invention is typically applied in a system comprising a first sensor arranged to be disposed in or outside the body of the individual for measuring aortic blood pressure Pa, and a second sensor arranged for measuring distal blood pressure Pd. Further, the system comprises a central monitoring device for monitoring the measured physiological variables and a communication link between the sensors and the central monitoring device for communicating signals representing the measured physiological variables from the sensors to the central monitoring device. The eavesdropping device is configured such that the communication interface is arranged at the communication link to communicate at least the signal representing the aortic blood pressure to a monitor of the eavesdropping device. Moreover, the receiver of the eavesdropping device is connected to the communication link, in parallel with the central monitoring device. The signal representing the aortic blood pressure Pa is communicated to the receiver via a high-impedance connection at the communication interface, and the receiver of the eavesdropping device is further arranged to receive the signal representing the measured distal blood pressure P from the communication link. By means of the blood pressure signals of the respective sensor, FFR can be calculated.
