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Are You Sure Your Heart’s In The Right Place?你能确定自己的心脏是在正确的位置上么？

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 stimulate¹ the heart. But then again, hearing the heartbeat is easier on the left.
在今天的《科学一刻》里，我们确信你的心脏在正确的位置上。可是具体是在哪里呢？心脏复苏课程向我们介绍了如何按压位于胸部中心的胸骨来复苏心脏。然而，心跳声在胸部偏左更容易听到。

What Gives?
心脏是什么样的？

Anatomically speaking, the heart is pretty much centered in the chest cavity, although it is tilted² to the left, and takes a bit more space from the neighboring left lung than the right.
从解剖学上说，心脏几乎是在胸腔正中的位置的，不过稍微向左倾斜，与右肺相比，它占据了左肺更多的位置。

To understand why the heartbeat’s easier to hear on the left side, we need to know about the four chambers⁴ of the heart.
为了理解为什么更容易从从左边听到心跳声，我们需要对心脏的四个腔有所了解。

Top Of The Heart
心脏上部

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.
心房是指位于心脏上部的两个小腔。心室是指心脏下部更大，肌肉更发达的两个腔。因为心房只需将血液压到心室即可，所以肌肉不需要那么发达。

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 chamber³ of the heart. It’s also closest to the chest wall, while the atria are farther back, tucked under the lungs.
右心室体积要更庞大，因为需要通过它将血液泵入肺中获取氧气。而左心室的任务最重——将血液泵入身体其他部分——因此也是心脏中肌肉最发达的肌室。左心室也是离胸壁最近的部分。而心房则离胸壁较远，藏在肺里。

Work That Heart
让心脏动起来

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.
也就是说左心室，这个在心脏中工作最重的肌室，不仅位于最左面，而且离胸壁最近。这就是尽管心脏基本是在胸部正中，你却能很容易的从左面听到心跳声的原因。