This is a process in which small (normally closed) arteries open up and connect two larger arteries or different parts of the same artery. They can serve as alternate routes of blood supply.

Everyone has collateral vessels, at least in microscopic form. These vessels normally aren't open. However, they grow and enlarge in some people with coronary heart disease or other blood vessel disease (such as in the case of stroke). While everyone has collateral vessels, they don't open in all people.

How does collateral circulation help people with heart disease?

When a collateral vessel on the heart enlarges, it lets blood flow from an open coronary artery to an adjacent one or further downstream on the same artery. In this way, collateral vessels grow and form a kind of "detour" around a blockage. This collateral circulation provides alternate routes of blood flow to the heart in cases when the heart isn't getting the blood supply it needs (myocardial ischemia) (mi"o-KAR'de-al is-KE'me-ah).

How does collateral circulation help people with stroke?

When an artery in the brain is blocked due to stroke or transient ischemic (is-KEM'ik) attack (TIA), open collateral vessels can (but not always) allow blood to "detour" around the blockage. This collateral circulation restores blood flow to the affected part of the brain. However, not all people can develop “collateral circulation,” so prevention of heart disease and stroke should always be the gold standard.

Related AHA publications:

• Your Heart and How It Works