The cardiovascular system includes the heart, blood vessels, and blood, and is responsible for circulating blood throughout the body. The heart is a muscular pump about the size of a fist that beats over 100,000 times per day to pump blood. Blood carries oxygen, nutrients, hormones, and waste products and helps regulate temperature, pH, and defend against toxins. The major components of blood are plasma, red blood cells, white blood cells, and platelets. Common cardiovascular problems include heart disease, stroke, and atherosclerosis. Risk factors for these diseases include tobacco use, diet, exercise, diabetes, and heredity.