Computer-implemented method for decomposing a resultant electric potential ( V wyp) forming the QRS complex in the electrocardiogram into partial potentials corresponding to the depolarization of specific areas (i) of the left ventricular muscle, in which decomposition is carried out in such a way that on the basis of the theoretical SFHAM model of electrical heart activity, mathematical functions describing changes in the partial potential values are determined, and then their parameters are selected so that the superposition of the values of these functions is as close as possible to the resultant potential ( V wyp) measured during the ECG test, wherein each of the partial potentials is described by two functions: V 1,i ( t) and V 2, i ( t), corresponding to the depolarization of a specific area of the left ventricular muscle, each of these functions has negative or positive values and one extremum, wherein the beginning of the emergence of these potentials ( t 0, i and t 0, i) and their end ( t k, i and t k,i) is considered the time at which the potential value is greater than its arbitrarily set minimum value, and the sum of the values of these potentials determines the electrical activity of the specific area of the left ventricular muscle, wherein the order of occurrence of the extrema is determined from the theoretical SFHAM model of electrical heart activity, and the positions of extrema are determined by: • making a series of transformations of the potential values for X Y Z coordinates in the orthogonal system, consisting in rotation of the coordinates in the range 0-90° with respect to two selected axes by α, β angles, • calculating, for each rotation angle, the positions of extrema of the partial potentials for each of the X Y Z coordinates, by using deconvolution and convolution, and a low-pass filter with parameters corresponding to the function describing the partial potentials, and then • selecting the angles for which the differences in the positions of extrema for each of the partial potentials in the XYZ system, respectively, are the smallest. wherein each of the partial potentials is described by two functions: V 1,i ( t) and V 2, i ( t), corresponding to the depolarization of a specific area of the left ventricular muscle, each of these functions has negative or positive values and one extremum, wherein the beginning of the emergence of these potentials ( t 0, i and t 0, i) and their end ( t k, i and t k,i) is considered the time at which the potential value is greater than its arbitrarily set minimum value, and the sum of the values of these potentials determines the electrical activity of the specific area of the left ventricular muscle, wherein the order of occurrence of the extrema is determined from the theoretical SFHAM model of electrical heart activity, and the positions of extrema are determined by: • making a series of transformations of the potential values for X Y Z coordinates in the orthogonal system, consisting in rotation of the coordinates in the range 0-90° with respect to two selected axes by α, β angles, • calculating, for each rotation angle, the positions of extrema of the partial potentials for each of the X Y Z coordinates, by using deconvolution and convolution, and a low-pass filter with parameters corresponding to the function describing the partial potentials, and then • selecting the angles for which the differences in the positions of extrema for each of the partial potentials in the XYZ system, respectively, are the smallest. • making a series of transformations of the potential values for X Y Z coordinates in the orthogonal system, consisting in rotation of the coordinates in the range 0-90° with respect to two selected axes by α, β angles, • calculating, for each rotation angle, the positions of extrema of the partial potentials for each of the X Y Z coordinates, by using deconvolution and convolution, and a low-pass filter with parameters corresponding to the function describing the partial potentials, and then • selecting the angles for which the differences in the positions of extrema for each of the partial potentials in the XYZ system, respectively, are the smallest.