Question

We learnt that heart is made up of cardiac muscles which are controlled by our brain. Then can we stop our heartbeat by commanding cardiac muscles to stop.

Answer 1

Smooth and cardiac muscle are under the control of the involuntary, or autonomic, nervous system and not the voluntary part of brain i.e it can't be directly controlled by us.
Hence cardiac muscles are also called involuntary muscles.
So we cant stop the heart by commanding it.

Hope this helps :)