Electrocardiographic Imaging (ECGI) is a new imaging technique that noninvasively images cardiac electrical activity on the heart surface. In ECGI, a multi- electrode vest is used to record the body-surface potential maps (BSPMs). Then, using geometrical information from CT-scans and a mathematical algorithm we construct the electrical potentials on the heart surface. The reconstruction of cardiac activity from BSPMs is an ill-posed problem. Some algorithms work well in sinus rhythm, but in arrhythmic conditions the reconstruction of the heart potential becomes worst. In this work, we present an iterative mathematical approach based on domain decomposition methods and test it on synthetically data generated using anatomical 43 years old women geometry for normal and fibrillating heart conditions.