Suffering left breast pain while walking or doing anything strenuous. the pain subsides while resting. i am only 27, could this be a heart issue?

Yes: I'm a skeptic with regard to chest pain in young adults because heart-related chest pain is unusual in the young but does happen. Your description is concerning. This could be a heart issue, but asthma or other lung pathology could also cause this. Other, more benign causes of chest pain are generally not associated with exercise, so a doctor visit is highly recommended here.