Activation wave front, indicated in light red, originating from the apex of the papillary muscle $S(t)$ at t = 10 ms and t = 40 ms. At 10 ms the initial anatomical vector points from apex to the base of the papillary muscle, but at 40 ms a significant part of the ventricular apex is already activated. The resulting anatomical vector points now from apex to base of the left ventricle, i.e. in the opposite direction.