FIELD : medicine. SUBSTANCE : group of inventions relates to cardiology. Computer method involves receiving an endovascular ECG signal associated with an endovascular device. Treatment of the endovascular ECG signal for a plurality of predetermined time periods to calculate the amplitude of the tooth R and spectral power for each given period of time. Determination of maximum amplitude of tooth R from multiple amplitudes of tooth R and corresponding maximum spectral power from multiple spectral powers. Associating maximum amplitude of the tooth R and maximum spectral power with a predetermined location in the heart or near it. Calculating the endovascular device location for each predetermined period of time based on the ratio of the amplitude of the tooth R to the maximum amplitude of the tooth R and the ratio of spectral power to the maximum spectral power and displaying the endovascular device location to the user. EFFECT : group of inventions enables maximum accurate non-invasive determination of the location of the end of the catheter tip in the heart or main vessels. 26 cl, 15 dwg