A computer-implemented method for determining Ventricular Far Field contribution in Atrial Electrograms of a patient, the method comprising: receiving a plurality of previously recorded electrical signals (ECGm, Fm, Gm, Hm, Bm, Cm, Dm) measured by a plurality of sensors (S1 to Sn) wherein the plurality of electrical signals relates to a plurality of locations in an atrium of the patient; determining a reference signal (RS, I, II, CS) measuring the electrical excitation of the patient's ventricles; selecting from the plurality of the received electrical signals such electrical signals which are recorded under one or more of the following conditions by verifying each of the three conditions: - the respective signals are recorded at locations inside the atrium where the respective sensor has no contact to the atrial tissue, - the respective signals are recorded, irrespective of the sensor location, during time intervals where the respective part of the atrium shows no electrical activity, - the respective signals are recorded, irrespective of the sensor location, during time intervals which comprise a plurality of heart beat intervals and are subject to subsequent spatial smoothing; and determining a spatio-temporal distribution of the Ventricular Far Field inside the atrium by approximating the spatio-temporal distribution based on signal data of the selected signals by using an approximation model, wherein the approximation model is computed on the basis of the selected signal data and allows for interpolation and extrapolation of the Ventricular Far Field contribution at locations where no sensor data has been recorded. receiving a plurality of previously recorded electrical signals (ECGm, Fm, Gm, Hm, Bm, Cm, Dm) measured by a plurality of sensors (S1 to Sn) wherein the plurality of electrical signals relates to a plurality of locations in an atrium of the patient; determining a reference signal (RS, I, II, CS) measuring the electrical excitation of the patient's ventricles; selecting from the plurality of the received electrical signals such electrical signals which are recorded under one or more of the following conditions by verifying each of the three conditions: - the respective signals are recorded at locations inside the atrium where the respective sensor has no contact to the atrial tissue, - the respective signals are recorded, irrespective of the sensor location, during time intervals where the respective part of the atrium shows no electrical activity, - the respective signals are recorded, irrespective of the sensor location, during time intervals which comprise a plurality of heart beat intervals and are subject to subsequent spatial smoothing; and - the respective signals are recorded at locations inside the atrium where the respective sensor has no contact to the atrial tissue, - the respective signals are recorded, irrespective of the sensor location, during time intervals where the respective part of the atrium shows no electrical activity, - the respective signals are recorded, irrespective of the sensor location, during time intervals which comprise a plurality of heart beat intervals and are subject to subsequent spatial smoothing; and determining a spatio-temporal distribution of the Ventricular Far Field inside the atrium by approximating the spatio-temporal distribution based on signal data of the selected signals by using an approximation model, wherein the approximation model is computed on the basis of the selected signal data and allows for interpolation and extrapolation of the Ventricular Far Field contribution at locations where no sensor data has been recorded.