sensing opening and closing of a heart valve in the heart of a mammalian subject, and generating a sensor signal representing said opening and closing of said heart valve, said heart exhibiting a heartbeat rate;

filtering said sensor signal to extract a signal component therefrom, as a filtered signal, in a frequency range much higher than said heartbeat rate;

squaring said filtered signal to obtain a power signal representing power of said filtered signal;

providing said power signal to an electronic detection unit and, in said electronic detection unit, measuring, in said power signal, a pre-ejection period of said heart as a function of the sensed opening and closing of said heart valve;

additionally in said electronic detection unit, measuring, in said power signal, a ventricular ejection time of said heart;

in said electronic detection unit, automatically determining an ejection fraction of the heart as a function of the measured pre-ejection period and the measured ventricular ejection time; and

emitting an electronic output signal from said electronic detection unit representing said ejection function.