This document discusses, among other things, an apparatus comprising an atrial sensing circuit, a ventricular sensing circuit and an atrioventricular (AV) delay adjustment circuit. The atrial sensing circuit detects a first fast atrial pace that concludes a timing interval that is shorter than or equal to a first threshold value. The ventricular sensing circuit detects a first condition that comprises a sensed intrinsic first fast ventricular contraction that occurs within a specified first period of a most recently detected first fast atrial pace. The fast ventricular contraction concludes a timing interval that is shorter than or equal to a second threshold value. The AV delay adjustment circuit attempts to decrease an AV delay at least in part in response to detecting the first condition. Other apparatuses and methods are disclosed.