A system for detecting a cardiac event in a subject, comprising: at least one electrode adhered to the subject to obtain an electrocardiogram of the subject's heart； the determination means configured to determine the viable myocardium mass in the heart of the subject by determining the size of the area under the QRS complex of the electrocardiogram integrating the QRS complex of the electrocardiogram to obtain the area under the QRS complex, and the means of obtaining configured to obtain the difference between the size of the QRS complex area of the electrocardiogram and the area size of a QRS complex of an electrocardiogram of the same subject obtained on a previous occasion at a different time in the subject's life from an identical electrode to generate an index to determine the onset of a cardiac event, where the means of determination to determine the size of the area under the QRS complex of the electrocardiogram and the means of obtaining to obtain the difference between the size of the QRS complex area of the electrocardiogram and the size of the area of a QRS complex of an electro cardiogram of the same subject obtained on a previous occasion at a different time in the subject's life are quantitative, and where said difference obtained by the means of obtaining shows a change in the viable myocardial mass in the heart of the subject over a period of time from the previous occasion at a different time in the subject's life.Un sistema para detectar un evento cardiaco en un sujeto, comprendiendo: al menos un electrodo adherido al sujeto para obtener un electrocardiograma del corazón del sujeto； los medios de determinación configurados para determinar la masa de miocardio viable en el corazón del sujeto mediante la determinación del tamaño del área bajo el complejo QRS del electrocardiograma integrando el complejo QRS del electrocardiograma para obtener el área bajo el complejo QRS, y los medios de obtención configurados para obtener la diferencia entre el ta
