Natural Factors L-Arginine - 500 mg - A non-essential amino acid involved in protein synthesis. It may help support a modest improvement in exercise capacity in individuals with stable cardiovascular disease (CVD). As a free-form amino acid, L-arginine is easier for the body to absorb and use than when consumed from food. L-arginine is a conditionally essential amino acid, which means although it can be manufactured by the body, during times of illness, stress, and recovery from injury, the body may need more than it can produce on its own. L-arginine plays a critical role in the production of nitric oxide, a substance that relaxes blood vessels, helping to improve blood flow. A deficiency of L-arginine can disrupt many cellular functions in the body, including those of the blood vessels. Natural Factors L-arginine is a great choice for people who want to improve their exercise capacity, are under high levels of stress, or are involved in intense physical training.