Synchronous contraction of the heart depends on regular propagation of the electrical impulse, which is maintained by generation of cellular action potentials and by flow of local electrical currents between excited and resting cells (Kleber et al. 2001). Alterations in the normal pattern of propagation lead to arrhythmias and loss of contractile function. Understanding the mechanisms of these arrhythmias has relied on visualization of activation spread using mapping techniques that involve measurements of electrophysiological parameters at multiple sites and reconstruction of their distribution patterns. Two main cardiac mapping methods are currently used. © Springer-Verlag Berlin Heidelberg 2005.