It then propagates out through both atria, including bachmann's bundle in the left atrium, and contracts both atria.

然后它传导到两个心房，包括通过Bachmann氏束到达左心房，并且导致两个心房的收缩。

Electrical impulses from the SA node spread throughout both atria and stimulate them to contract.

窦房结发出的电脉冲扩散到整个心房并刺激它们收缩。

The SA node is actually only found in your right atrium, but its signal quickly spreads to the left atrium, and this allows both atria to contract at the same time.

SA结实际上只存在于右心房，但它的信号迅速扩散到左心房，这使得两个心房同时收缩。