What Causes Intermittent Stinging Pain In Heart?

Hi, my name is janay. about every month i get a stinging feeling in/on my heart, out of no where. when i inhale is when it begans. to stop the pain i usually have to hold my breath for about 15 seconds. but the pain is REALLY sharp and hurts really bad. I was born with a heart murmur but im not sure wether it held or not. Can you please tell me why this is happening or what it is? Thank you very much :-)