I recently had this feeling for 3 days on and off. Twitching in middle of chest, right below ribs. Even woke me up one night, if I put my hand there I could feel it for a second, then it would stop. It felt just like it does when my eye muscle twitches, but much, much stronger because it was a chest area muscle, very strange feeling. I already had an appointment to see my doctor for another symptom of feeling fatigued. The twitching in my chest had gone away, but I told my doctor about it anyways.
She ran tests for thyroid and anemia. Turns out I'm very anemic, so now I'm taking iron pills. I'm assuming the twitching was a side effect of this. It is NOT a heart condition, so don't freak yourself out. Make sure you are taking plenty of vitamins, it will go away.