HEART STIMULATOR
A heart stimulator for multi-site stimulation of a patient's heart (6) comprises a pulse generator and a measuring device (24, 26, 28, 30) for measuring a physiological cardiac parameter and delivering a corresponding output signal to a control unit (32, 34) for controlling time intervals between pulses delivered to different stimulation sites in the heart depending on the output signal according to a predetermined criterion. The measuring device comprises a ring-shaped electrode sized to fit within a blood vessel for the perfusion blood flow of the patient's heart, a counter electrode intended to be brought into contact with the blood, and a measuring unit (26) adapted to measure the voltage or current between the electrodes to determine therefrom, as the physiological parameter, the perfusion blood flow in said vessel.