A method and apparatus for analyzing the electrical activity of the heart by Body Surface Potential Mapping (BSMP) in which an array of electrodes are applied over the thoracic region of a subject's body for producing measurements of the electrical signals generated in the thoracic region, and the measurements are processed for indicating certain electrical events in the subject's body. The array of electrodes are utilized to measure only the times of crossing of the electrical signals over a preset threshold.