Gastrc issues are more likely
Thanks for query,
As you age is just 31 chances of it being cardiac are too low unless you are a chronic smoker or a tobacco abuser.
So if you are a nin smoker go for simple ecg.
In case you are smoker 2 d echo should be done.
if these tests are normal you are having acid peptic reflux disorder or gastritis
It cause soft tissue injury
and inflammation in gut wall and esophagus
causing pain of nature you described.
Sternum and nearby arear are usually involved.
has to be done to ruke out the cause.
For time being would suggest you to take Omeprazole
40 mg once daily with a glass of chilled milk.
Take any over the counter antacid syrup along with it.
Follow up with reports!