Reconstructing electrograms, whose experimental registration requires an invasive access, by computational way on unipolar ECGs recorded at 80 and more points of the chest surface. On the set of surface electrocardiograms for each discrete moment of the cardiocycle, values of the heart electric field potential at points of ECG-recording are determined, and a value of the electric field potential at each point of the chest surface is calculated by interpolation. Based on data of any visualization methodology, boundaries of chest and lungs surfaces and of the heart epicardial surface are determined. Further, a continuation of the electric field potential over the whole chest surface up to the heart epicardial surface with taking into account differences in electroconductivity of large anatomical structures of the chest is performed by computational way based on solution of the Cauchy problem for the Laplace equation in a piecewise-homogenous medium.