Normally, an electrical signal starts at the sinoatrial or SA node in the right atrium.

通常，电冲动从位于右心房的房开始。

And those fast, leaky cells are found in the sinoatrial node, or the SA node, up in the right atria.

这些快速渗漏的细胞位于房，或 SA ，位于右心房上方。

The starting point of the intrinsic conduction system is the sinoatrial node, or SA node.

在传导系统的起点是房。

In a healthy heart, the sinoatrial node or SA node initiates all electrical impulses in the atria.

在健康的心，房（SA）产生心房的所有电脉冲。

So, if we simplify this heart a little bit, normally, the sinoatrial node or SA node sends an electrical signal that propagates out through the walls of the heart and contracts both upper chambers.

如果我们稍稍简化一下心，正常时，房发放一次电信号，传遍心壁，且上腔室（心房）也收缩。