CBSE Class 9 Answered

In mentally retarded people, the heart is functioning well, but they are not completely alright. This is because heart is not the controlling centre of our body. Since their brain is not alright, they are not ok.

But remember that heart is a very vital organ of our body. Severe problems in heart can lead to the death of the person, even if the brain is functioning well. But this does not change the fact that the body functions are controlled by the brain, though for the complete well being of the body, all  the organs, especially the vital ones should function well.