a device for detecting embolus uses ultrasonic signals reflected on a fluid flow in a body . the device features a first ultrasonic unit for receiving a first signal generated in a first position in a vessel and a second ultrasonic unit for additional reception of a second signal generated in a second position in the body . the device also features a detector unit for detecting the embolus . the detector unit is triggered only if the time interval between the characteristic changes in the first and second signal , corresponding to a possible embolus , exceeds a minimum value , or if the characteristic signal change occurs in one of the signals only .