Day and night, the muscles of your heart contract and relax to pump blood throughout your body. When blood returns to the heart, it follows a complicated pathway. If you were in the bloodstream ...

Day and night, the muscles of your heart contract and relax to pump blood throughout your body. When blood returns to the heart, it follows a complicated pathway. If you were in the bloodstream ...

A wave of contraction spreads across the heart - to the left atrium and then to the ventricles. This enables the ventricles to contract together. Sometimes, the rhythm of the heart's natural ...