1. A method of diagnosis of heart failure, the method comprising: collecting, using an implantable device, 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 physical parameters, variation of activity, and variation of hemodynamic phases between phases of effort and phases of recovery; generating an in-suspicion model-cycle and an off-suspicion model-cycle based on the reference episodes; and determining whether to generate an early heart failure alert, based on a difference between the in-suspicion model-cycle and the off-suspicion model-cycle.