You could just have a leaky valve that is causing angina. But, to be on the safe side, please see a cardiologist. A leaky valve usually isn't life threatening, but can cause problems as you age. - I have a leaky mitral valve which may or may not need to be replaced some day. Meanwhile, I just take the meds my Cardiologist prescribed and I am doing okay. - I hope and pray that you will be okay also.
Go see a cardiologist asap... could be serious
as you are not aware it maybe a good idea to have it checked out, however it sounds like a pulled muscle, have you lifted anything heavy recently or done any heavier than usual work?