Pacemaker with improved detection of atrial fibrillation

The pacemaker comprises at least one atrial sensor for sensing atrial signals and a ventricular sensor for sensing ventricular signals. A pacing generator produces at least one of a ventricular and atrial pacing signals in accordance with a command signal. An atrial processor (100), receiving the atrial signals, includes an analyser (104) for determining peak amplitudes of the atrial signals and a normal sinus rhythm value of the peak amplitudes, and for determining a change in a variability and deviation of the normal rhythm value. The atrial processor is further provided to detect new state of the atrium by analysing the change in variability and deviation of the normal sinus rhythm value. A controller (106) receives indication of the atrial and ventricular signals and the new atrial state and generates in response the command signal on the basis of the new atrial state.