1. A method of diagnosis of heart failure, the method comprising: collecting, using an implantable device, a plurality of reference episodes, the reference episodes comprising at least one of: electrical activity signals of a myocardium; myocardium hemodynamic activity signals, or indicators reflecting variation of parameters between phases of effort and phases of recovery, wherein the parameters comprise at least one of physical parameters, activity parameters, or hemodynamic phase parameters between phases of effort and phases of recovery; analysing, using the implantable device, the plurality of reference episodes based on predefined criteria to assign each of the reference episodes an in-suspicion marker or an off-suspicion marker, wherein the in-suspicion marker indicates a suspicion that the reference episode is associated with cardiac decompensation, wherein the off-suspicion marker indicates a suspicion that the reference episode is not associated with cardiac decompensation, and wherein the reference episodes assigned the in-suspicion marker and the reference episodes assigned the off-suspicion marker are interspersed within the plurality of reference episodes; generating, using the implantable device, an in-suspicion model-cycle based on data associated with a plurality of in-suspicion reference episodes to which the in-suspicion marker has been assigned; generating, using the implantable device, an off-suspicion model-cycle based on data associated with a plurality of off-suspicion reference episodes to which the off-suspicion marker has been assigned; and determining, using the implantable device, whether to generate an early heart failure alert based on a difference between the in-suspicion model-cycle and the off-suspicion model-cycle.