Argit (Ben 10) is able to stop his own pulse to play dead.
Tim Drake (DC Comics) learned a "possum reflex" from Batman to slow his heartbeat in order to fake his death or restrict blood loss.
Using Gear Second, Monkey D. Luffy (One Piece) speeds up his heartbeat to increase blood flow throughout his body.
Richard B. Riddick (The Chronicles of Riddick) slows his heartbeat to evade detection by dogs.
Cotton Hill (King of the Hill) learned how to regulate his own heartbeat to feign death while at a Japanese POW camp.
Makoto Naegi (Danganronpa 4: Keyknives Nobodies Connections & Hearts) was born with Cardiopulmonary Powers Which allows him to Supernaturally Manipulate Hearts in an Inhuman Sense When Facing Off Against Junko Enoshima in a Trial He Could Hear her Heartbeats filled with Despair and When Kyoko died He couldn't feel her Heartbeat Regulation whatsoever
Through martial arts training and meditative breathing techniques, Bruce Banner (Marvel Cinematic Universe) learned to control his heart rate, either slowing it to prevent himself from transforming into the Hulk...
...or speed it up to transform at will.
Lord Death Man (DC Comics) can slow down his heartbeat to the point he can mimic the feel of death.