A computer-based method for positioning an endovascular device in or near the heart using electrocardiogram (ECG) signals is provided. The computer-based method includes receiving an endovascular ECG signal, associated with an endovascular device, including a plurality of waveforms, each waveform having at least a P-wave component, processing the endovascular ECG signal, over a plurality of predetermined time periods, to calculate a P-wave amplitude and a spectral power for each predetermined time period, determining a maximum P-wave amplitude from the plurality of P-wave amplitudes, and an associated maximum spectral power from the plurality of spectral powers, associating the maximum P-wave amplitude and the maximum spectral power with a predetermined location in or near the heart, calculating a location of the endovascular device, for each predetermined time period, based on a ratio of the P-wave amplitude to the maximum P-wave amplitude and a ratio of the spectral power to the maximum spectral power, and displaying the location of the endovascular device to a user.