I got a sharp pain in my heart. it came out of nowhere and then went away after. what was it?

Many possibilities: Chest pain can come from many causes including heart, lungs, esophagus, rib cage and others. Not knowing your age, health history, family history, smoking history, cholesterol level, and additional information specific to this pain, it is impossible to tell exactly what is causing this pain. Best to see your family doctor or internist for a definitive answer as to the source of your pain.

Sharp pain : More details are needed. Use anatomy for the location of the problem like left chest, mid-chest (not the heart), any associated symptoms. Usually, "sharp" chest pain is from the chest wall (ribs, muscles, and ribs)