Answer:
A VSD allows oxygen-rich (red) blood to pass abnormally from the left ventricle through the opening in the septum.
Step-by-step explanation:
The septal wall prevents the mixing of blood between the two ventricles of the heart. A VSD allows oxygen-rich (red) blood to pass abnormally from the left ventricle through the opening in the septum. Then it mixes with oxygen-poor (blue) blood in the right ventricle.