Expert answer:
Because you are alive and this is part of your defense defense system attack, the adrenaline rush in risky situations makes your heart race to improve its ability to respond to stimuli that seem offensive to you.
Because sometimes my heart speeds up when I get nervous or take a fright?
Because you are alive and this is part of your defense defense system attack, the adrenaline rush in risky situations makes your heart race to improve its ability to respond to stimuli that seem offensive to you.