Beavers can hold their breath for as long as 15 minutes. However, they typically remain underwater for no more than five or six minutes. Dives generally last less than 30 seconds and are usually shallow, at less than . Beaver tissue contains less myoglobin than fully aquatic mammals. When diving, their heart rate decreases to 60 beats per minute, around half its normal function, while blood flow to the brain increases. Beavers also have a high tolerance for carbon dioxide in their body. When surfacing, the animal can replace 75 percent of the air in its lungs in one breath, compared to 15 percent for a human.