Seals get their hearts racing to detox after foraging trips at sea

Diving is physiologically challenging for marine animals. Long and deep dives can trigger "anaerobic" (oxygen-less) metabolism in organs other than the heart and brain that causes lactic acid to accumulate. Even though diving animals typically have evolved tricks to avoid "the bends," nitrogen bubbles may nevertheless build up in their blood. They tend to recover from these stresses while swimming at the surface for prolonged periods.