The heart pumps harder and blood pressure rises during a fight-or-fight response. This response is due to

Question

fatir5 · Answer

This response is due to any perceived harmful attack, stress situation or when in a state of combat. Heart pump harder, vessels become narrower and muscles become tighter. So now you can relate if you would like to fight something or escape. Hence the "Fight or flight" situation.

aaronq · Answer

the answer to this can vary depending at the certain level you're looking at, but i guess if you're looking for a specific molecule it would be, ultimately, adrenaline.

anonymous · Answer

Sympathetic responses => adrenaline