16atwarNOT,

Thanks for your question.  Your symptoms are unlikely to be caused by your heart.  Pain associated with heart disease if not affected by your breathing.  In addition, 16 year olds are at very low risk for heart attacks, though they do rarely occur.

Your problem could be a muscular problem in your chest wall, such as a pulled muscle or bruised rib cage.  In some cases a process that irritates the diaphragm (breathing muscle) can cause pain in a shoulder.  This could be caused by an abdominal problem, or a lung problem. 

It's difficult to answer this question with the benefit of examining you.  I suggest you make an appointment with your doctor for his evaluation.  After examining you, he will be able to make a determination of the cause of your discomfort.

Best wishes.

Martin Cane, M.D.