Atresia
Complete obstruction to a valve or blood vessel, so that blood cannot get past this point in the circulation and has to take an alternative route.
Cardiac
Atrial Fibrillation [AF]
This is a common abnormal heart rhythm that happens when electrical impulses fire off from different places in the atria (the top chambers of the heart) in a disorganised way. This causes the atria to twitch, and results in an irregular heartbeat or pulse. Atrial fibrillation is a major cause of stroke.
Arterioles
Small, muscular branches of arteries. When they contract, they raise resistance to blood flow, and blood pressure in the arteries increases.