An actual heart attack
) before the age of 50 is extremely rare and at 21 even rarer.
Everyone will experience "palpitations" in their lifetime at some point or another. This seems to just of been a one day occurrence from what you stated.
This is unlikely to have any clinical significance as this is just one simple day.
Palpitations are usually not indicative of major events happening. Heart attacks usually have a more discomfort feeling in the chest area than palpitations.
This, however, could be indicative of a heart problem.
You might actually have something wrong with you, but emergency departments are set up to assess the potential of a life-threatening emergency happening. They will not do further testing such as echocardiogram
of the heart) if they don't find any problems with simple tests such as ECG/EKG (same thing).
The best option for you at this point is to make an appointment with your local doctor if symptoms persist or if you are still worried about it and see what your local doctor thinks. They will listen for a murmur and determine if more testing such as echocardiogram is needed.
I'm not saying that you don't have potential to have an actual cardiac event, because you do, just like every other person. Don't ever hesitate to go to your local ER if you feel the need because it is the law that they evaluate your symptoms for any life-threatening possibilities.
Best of luck to you!
NOTICE-- No one on this thing can diagnose you with anything including PVC's. PVC's are just more common but what happens to others is not necessarily what is happening to you! Never take a diagnosis off of the internet.