Abstract: A method includes, during arrhythmia occurrence, acquiring multiple sets of reference coronary sinus electrophysiological (CS-EP) signals with a first catheter in coronary sinus (CS) of a heart of a patient, while measuring multiple respective reference CS locations of the first catheter. One or more intra-cardiac electrophysiological (IC-EP) signals are acquired with a second catheter located in a cardiac chamber of the heart, while acquiring actual CS-EP signal with first catheter, and while measuring an actual CS location of first catheter. Using reference CS locations, reference CS-EP signal is identified whose reference CS location is nearest to actual CS location of the first catheter. A signal-stability measure between actual CS-EP signal and identified reference CS-EP signal is estimated.