Exemplary methods and apparatuses are disclosed that provide for determination of an atrio-ventricular delay on a beat-to-beat basis by determining a P-wave duration from electric signals corresponding to electric potentials in a heart, and determining the atrio-ventricular delay on a beat-to-beat basis such that the atrio-ventricular delay for an individual heart cycle depends on the P-wave duration of a same or an immediately preceding heart cycle.
