| The heart is a muscle and needs blood. But because the heart is the only muscle
that supplies blood to itself, it has to stay in good physical condition, as do
the two coronary arteries through which blood travels. Healthy arteries let the
blood flow freely. They expand to allow more blood through when you're active.
When you walk up a flight of stairs, the heart beats faster to supply the
additional oxygen your muscles need for the extra effort. When more oxygenated
blood is needed and your heart can't supply enough blood to itself or
elsewhere, there are three things that commonly happen: angina, heart attack or
stroke.
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