FitBit's heart monitoring devices are called "wildly inaccurate" in a lawsuit accusing the company of false advertising.

Devices sold by the leading maker of fitness trackers "are mis-recording heart rates by a very significant margin" while on the brink of causing health risks for users, according to a complaint filed this week in a San Francisco federal court.

FitBit devices have been accused of mis-recording heart rates.

A Colorado woman alleges that her Charge HR device under-reported her actual heart rate by 50 per cent, as recorded manually by her personal trainer after a period of intense exercise.

"Scores of customer complaints confirm these are not isolated incidents," according to to the complaint, which was brought as a class action on behalf of other customers.