1. A method for localizing an activation site of origin to an area of the heart comprising: generating a plurality of patient-specific coefficient parameters relating a location of an activation site to integrals of ECG signals during an ablation procedure by i) for several pacing sites, the number of pacing sites being more than the number of patient-specific coefficient parameters, obtaining a plurality of simultaneously recorded ECG signals from a plurality of leads, from a patient; ii) calculating an integral of the signal recorded from each of a subset of the plurality of leads; iii) obtaining the three-dimensional location of the activation site from an electroanatomical system; and iv) applying a linear regression with intercept to the integrals and to the three-dimensional location of the collected pacing sites to obtain the plurality of patient-specific coefficient parameters; obtaining a plurality of simultaneously recorded ECG signals of interest from a plurality of leads, corresponding to those used to derive the patient-specific coefficient parameters, from the patient; calculating an integral of the ECG signal recorded from each of a subset of the plurality of leads for the ECG signals of interest; applying the patient-specific coefficient parameters to the integrals for the ECG signals of interest to obtain an estimated activation site; and displaying the estimated activation site as a point on a model of a heart.