Foxglove is the source of digitalis which is used to treat problems with the heart. No one who isn't a trained herbalist should ever, ever try to use herbal preparations of foxglove for any reason whatsoever as using it improperly can cause death from heart failure.
Always remember that just because herbs are natural does not mean that they are safe. Used incorrectly many useful herbs can also cause deadly effects. And never use herbs in conjunction with other medications without checking first with your doctor as herb/medicine interactions can cause serious problems.