The heart is the body's hardest-working muscle. Whether you're awake or asleep, or exercising or resting, your heart is always at work. It pumps blood through arteries to deliver oxygen to organs and ...
During an average lifetime, the heart beats more than 2 billion times. To you, it might just be a steady “lub-dub” that speeds up under pressure and slows as you drift to sleep. But behind that rhythm ...
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