1. A heart stimulating system for stimulating at least a ventricle of a heart comprising: a stimulation pulse generator adapted to generate electric stimulation pulses and being connected or being connectable to at least a ventricular stimulation electrode configured to deliver electric stimulation pulses to at least a ventricle of a heart; an atrial sensing stage connected or being connectable to an electrode configured to pick up electric potentials inside at least an atrium of said heart, said atrial sensing stage being adapted to sense an excitation or a contraction of atrial myocardium; a ventricular sensing stage connected or being connectable to a second electrode configured to pick up electric potentials inside at least a ventricle of said heart, said ventricular sensing stage being adapted to sense an excitation or a contraction of ventricular myocardium; a memory for AV-delay values; a control unit that is connected to said memory, at least one sensing stage and to said stimulation pulse generator, said control unit adapted to trigger said stimulation pulse generator to generate ventricular stimulation pulses that are timed based on said AV-delay values stored in said memory and to acquire atrioventricular interval samples representing time interval AsVs or ApVs between an atrial sense event As or an atrial stimulation pulse Ap, respectively, and an immediately following ventricular sense event; and, an atrioventricular interval timing analyzing unit that is part of said control unit or that is connected to said control unit configured to receive atrioventricular interval samples from said control unit wherein said atrioventricular interval timing analyzing unit is adapted to generate at least one histogram based on said atrioventricular interval samples received from said control unit and analyze said at least one histogram to determine a m th q-quantile atrioventricular interval based on counts in said at least one histogram with 0<m<q.