In an implantable heart stimulating device, system and method, a control
circuit has first and second circuits for sensing and pacing. The first
circuit can be connected to a first electrode member suited to be
positioned in or at a first ventricle of the heart. The second circuit
can be connected to a second electrode member suited to be positioned in
or at a second ventricle of the heart. The control circuit is able to
detect whether signals sensed by the second circuit are likely to be far
field signals. The control circuit performs this detection by at least
determining whether, during a predetermined time (length, more signals
are sensed by the second circuit than by the first circuit.