Muscle Might is an herbal L-arginine complex that increases load capacity, strength and endurance. It works because L-arginine makes Nitric Oxide which enlarges your capillaries, veins and arteries. The purpose is to deliver more oxygen and nutrients to the muscles you are trying to build. But it also puts an extra load on your heart because more blood is being pumped. When taken in the amounts you are directed to take there have been no reports of adverse side effects. Understand that if you have high blood pressure or any health issues you should consult your physician before taking any supplements and certainly before increasing any endurance reps.