In the throws of a racing heartstrings (185–220 pulse oximeter) what should be done to stop it from beating so fast? Er visit or wait it out?

ER if prolonged. You can try some bagel maneuvers (bearing down, submerging your head in a bucket of cold water), but if the heart racing continues for more than 30 sec or is associated with shortness of breath, chest pain or passing out, go to er immediately (don't drive - have someone or ems take you).
Depends. If you are having chest pain, short of breath, dizziness or have known heart disease, go to the er. If you are young and healthy, you could try putting your face in ice water. If this doesn't work, see a doctor.