High cholesterol levels. Computer artwork of balls of cholesterol in a blood vessel. When there are high levels of low density lipoprotein (LDL) cholesterol in the blood it builds up on the sides of blood vessels hardening them, a condition named atherosclerosis. This narrows the blood vessels and may even block them, causing a heart attack if the blocked vessel is in the heart, or a stroke if it is in the brain. A group of drugs called statins can be taken to lower LDL-cholesterol. Statins inhibit the enzyme in the liver that synthesises LDL-cholesterol. They also act on the blood vessels, reducing the risk of hardened vessels rupturing or becoming blocked.