This is the relevant information: The interventricular septum, is the stout wall separating the ventricles, the lower chambers of the heart from one another.
This justifies what answer for what question? Q & A:
Passage: The interventricular septum, is the stout wall separating the ventricles, the lower chambers of the heart from one another.

Question: Based on this passage, what is the function of the interventricular septum in the heart?
separating the ventricles , the lower chambers of the heart from one another