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Four valves keep the blood moving in the appropriate direction. Two of the heart's valves separate the right and left atrium from the right and left ventricles. Two other valves separate the right ventricle from the pulmonary artery and the left ventricle from the aorta.
四组瓣膜使血液以合适的方向流动。其中两组将左右心房与左右心室分开。另两组瓣膜分别将右心室到肺动脉、左心室和主动脉分开。
During a normal heartbeat, oxygen-poor blood returning from the body enters the right atrium through the vena cava. The right atrium contracts, pushing blood through the tricuspid valve and into the right ventricle.
在一个心动周期中，机体的乏氧血液通过腔静脉进入右心房。右心房收缩，将血液通过三尖瓣推入右心室。
Next, the right ventricle contracts to pump blood through the pulmonic valve and into the pulmonary artery, which connects to the lungs. At the same time, oxygen-rich blood returning from the lungs is delivered to the heart through the pulmonary veins.
接着，右心室收缩，将血液通过肺动脉瓣推入肺动脉，肺动脉连接到肺。与此同时，肺内富含氧气的血液通过肺静脉进入心脏。
The pulmonary veins empty into the left atrium, which contracts to push oxygen-rich blood through the mitral valve and into the left ventricle. The left ventricle contracts, pushing the blood through the aortic valve and into the aorta, which distributes blood to arteries throughout the body.The heart is supplied with blood through the coronary arteries, which branch off the aorta.
肺静脉流入左心房，左心房收缩，将富含氧气的血液通过二尖瓣推入左心室。接着，左心室收缩，将血液通过主动脉瓣推入主动脉，主动脉将血液运送到全身动脉。心脏的血液供应来自冠状动脉。主动脉分出冠状动脉。
