i t t t s u g s a c f B Starting from the early 1930s with pioneering studies such as those by Barker et al, the mapping of the surface ocal activation times of the human cardiac tissue, i.e., the ocal timings of the excitatory process, has been a key lement in electrophysiological studies aimed at identifying rrhythmogenic sources. In common clinical procedures, this is usually achieved invasively by measuring the local electrograms using epicardial or endocardial contact leads. Aside from the clinical and financial drawbacks of n invasive catheterization surgery, the important informaion regarding the intramural electrical activity can only be oosely inferred from the surface measurements and thus emains largely unknown. Three dimensional (3D) mapping f the cardiac electrical activity has so far been preliminary nd experimental, and mostly inapplicable to intact hearts. lthough arrays of plunge electrodes can be used to map the nstantaneous distribution of the excitatory process in the D cardiac tissue, this technique suffers from substantial echnical limitations, is restricted to isolated hearts, and herefore cannot be applied in surgery. Recent attempts to perform 3D cardiac mapping include trans-illumination, whereby the subendocardial and subepicardial electrical activity can be accessed via optical mapping in combination with photon diffusion theory, yet this technique is relevant only to thin tissues, requires toxic dyes, and can only be applied in laboratory setups. A major step toward a clinially feasible noninvasive mapping of the cardiac electrical ctivity is the electrocardiographic imaging method, which nvolves the solution of a highly ill-conditioned inverse roblem, thus providing relatively low spatial resolution of he activation waves, and which is highly sensitive to noise. dditionally, it requires an auxiliary imaging modality that ither utilizes ionizing radiation (e.g., X-ray computed toography) or is costly (e.g., magnetic resonance imaging). evertheless, electrocardiographic imaging has been shown n preliminary research to be clinically informative to some xtent and is still under validation studies. Despite the ongoing efforts to map the cardiac 3D electrical excitatory process, no satisfactory technologies have