Yes it is true, you can hurt your pectoral muscles.
At your age i would say it's probably not "heart" related. If your very worried i would ask the doctor for a stress test
A stress test determines ischmia and how much your heart works when exercising. it's a great test to tell a doc if you have any heart disease
. Another test is an echo cardiogram which looks at the chambers of your heart to see the blood flow of the valves, to check for stenosis.
I wouldn't be worried, if your doc thinks your fine and you have no positive family history. I would do an stress test if:
-you have sharp stabbing pains with exersion (with activity)
- have shortness of breath
, pain shooting down your left arm, shoulders or jaw
-weakness, increasingly tired
If not it's probably just a pulled muscle (which has happened to me when i work out my chest). Give it a few days and see what happens but if you have many of the symptoms i described go back to your doc and explain to him again!