Determination of site of origin (SoO), intramural conduction (IC) and exit site (ES) with an endocardial focus. Top panel shows isopotential maps at SoO (left) and ES (right). Lower panel shows corresponding virtual electrograms: first time cursor position represents SoO which is defined as the very earliest activation on the isopotential map whereas second cursor position represents ES which is defined as spread of activation on the isopotential map corresponding to the maximal negative deflection (steepest component) of the virtual electrogram. The time span between these two cursor positions reflects IC. Note that only minimal deflections of reconstructed electrograms are visible at the site of origin. See text for further details