Strain left side of chest?

[Charles Price]

Hey I went for a brisk walk this morning, I was smoking and felt a strain on left side under my nipple, does it sound like angina? or indigestion from smoking and walking? I'm 21 years old and have had several EKG's and been giving the clear. I do plan to book in for an echo soon for a piece of mind. I hear usually angina related pain is usually the centre of the chest? Should I really be cornered about having a heart defect at 21?

[NixonRulz]

I am not sure what it would be but I am fairly certain that it has nothing to do with any heart issue.
Especially after being checked out in the recent past

Just your mind getting the better of you