A system and method of identifying focal sources is presented. The methodcan comprise detecting, via sensors, electro-cardiogram (ECG) signals overtime,each ECG signal detected via one of the sensors having a location in a heartandindicating electrical activity of the heart, each signal comprising at leastan R waveand an S wave； creating an R-S map comprising an R-to-S ratio for each of theECGsignals, the R-to-S ratio comprising a ratio of absolute magnitude of the Rwave toabsolute magnitude of the S wave； identifying, for each of the ECG signals,localactivation times (LATs)； and correlating the R-to-S ratios for the ECG signalsonthe R-S map and the identified LATs and using the correlation to identify thefocalsources.
