Abstract: A device for biological tissue stimulation continually undertakes an evaluation of the stimulation sensitivity of the biological tissue to be stimulated, so that the stimulation energy can be set at a level just high enough to evoke a tissue response. Each evaluation ensues by stimulating the tissue with progressively lower energy levels, until no tissue response is detected. In order to improve matching of the stimulation energy to the varying stimulation sensitivity, and to keep the number of unsuccessful stimulation attempts, which occur during each evaluation, low, a device is disclosed wherein calculation of the stimulation sensitivity occurs at periodic time intervals, each time interval having a duration which is selected dependent on the variation in the stimulation sensitivity between the two most recently occurring calculations of the stimulation sensitivity. The device may be, for example, a heart pacemaker. A method for tissue stimulation is also disclosed.