英語聽力文摘684 心臟的正確位置你知道么

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On today’s Moment of Science, we’re sure your heart’s in the right place. But where is it exactly?!? CPR classes show how to press on the sternum, in the center of the chest, to stimulate the heart. But then again, hearing the heartbeat is easier on the left.

What Gives?

Anatomically speaking, the heart is pretty much centered in the chest cavity, although it is tilted to the left, and takes a bit more space from the neighboring left lung than the right.

To understand why the heartbeat’s easier to hear on the left side, we need to know about the four chambers of the heart.

Top Of The Heart

The atria are the two small chambers at the top of the heart. The two ventricles are the larger, more muscular chambers on the bottom. Because the atria simply pump blood down to the ventricles, they don’t need to be that muscular.

The right ventricle needs to be more bulky, because it pumps blood out to the lungs to get oxygen. But the left ventricle has the most difficult task–pumping blood to the rest of the body–so it’s the most muscular chamber of the heart. It’s also closest to the chest wall, while the atria are farther back, tucked under the lungs.

Work That Heart

That means that the left ventricle, the hardest-working chamber of the heart, is not only farthest to the left but also closest to the chest wall. And that’s why it’s so easy to hear your heartbeat on the left, even though the heart is nearly centered in the chest.