Nitric oxide is made by the blood vessels’ lining, or endothelium. The endothelium is exquisitely sensitive to the physical and chemical conditions inside our blood vessels. When the endothelium senses heart-healthy conditions, such as physical activity and low cholesterol, it releases more nitric oxide. And that’s a very good thing. Nitric oxide expands the blood vessels, increasing blood flow and decreasing plaque growth and blood clotting.