Give a stream of consciousness and then the final answer. The sinoatrial node (SA node), also known as sinus node, is a group of cells located in the wall of the right atrium of the heart. These cells have the ability to spontaneously produce an electrical impulse (action potential; see below for more details), that travels through the heart via the electrical conduction system (see figure 1) causing it to contract. In a healthy heart, the SA node continuously produces action potential, setting the rhythm of the heart and so is known as the heart's natural pacemaker. The rate of action potential production (and therefore the heart rate) is influenced by nerves that supply it.

Based on this passage, where is the sa node located in the heart?
The relevant sentence in the passage is: The sinoatrial node (SA node), also known as sinus node, is a group of cells located in the wall of the right atrium of the heart.
So, the final answer is the wall of the right atrium.