It sounds like you have Mitral Valve Prolapse
) which is when the blood in your heart "backs up" and feels like flutters in your chest. Mild cases (such as what yours sounds like) can be treated with low doses of Beta Blockers like Nadalol. You need to see your doctor and describe your symptoms to him/her and ask for a stress test
and/or a referral to a Cardiologist.