Normally the heart contracts and relaxes between 70 and 80 times per minute, each heartbeat filling the four Chambers inside with a fresh round of blood.
通常每分钟心脏会收缩和扩张70至80次，每次心跳会给四个心室供应一股新鲜的血液。
Normally the heart contracts and relaxes between 70 and 80 times per minute, each heartbeat filling the four Chambers inside with a fresh round of blood.
通常每分钟心脏会收缩和扩张70至80次，每次心跳会给四个心室供应一股新鲜的血液。
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