Your heartbeat is what keeps you alive and breathing by transporting blood so without it you are dead.
This justifies what answer for what question? Q & A: 
One of the following sentences is nonsensical. Which one is it?
Options:
- Sentence A: "If your heartbeat stops then you are classed as dead."
- Sentence B: "You are still alive if you do not have a heartbeat."

Sentence B