The invention relates to a method for controlling a reversible electrical machine (14) coupled to a heat engine (13). The electrical machine comprises a field winding (20) which is fed by an excitation current and an armature comprising a plurality of phase windings (22) fed by phase currents. According to the invention, the excitation current of the electrical machine is controlled according to the instantaneous rotational speed of the machine and the torque of the heat engine. According to other characteristics, the excitation current is equal to a pre-determined nominal current when the torque of the engine is resistant and the instantaneous speed is slower than a first pre-determined rotational speed, and is weaker than the nominal current when the torque of the engine is driving or the instantaneous speed is faster than the first speed.