Can the power of attorney also be the heir?

Yes, you can be his POA. You can also be the executor of the will. There is no legal conflict of interests there. Family members are often POAs, executors, and heirs.

And, just like you all taught me, the POA ends upon death, right?

I'm another heir and proxy, like Windy.

The law dictionary describes an "heir" as follows: one who acquires property upon the death of another, based on the rules of descent and distribution, namely, being the child, descendant or other closest relative of the dear departed.

Yes. I have POA for my parents and I am an inheritor in the as well as executor of the will. It's very common.