There is a irregular pulse happening below my breast, somewhat in between my rib cage but it feels as if it's under neath the top left, (my left) near my heart, part if my rib cage... I can't feel it externally when i put my hand on it but i can feel it internally & it's very irregular, my hearts beating pulse is very regular & perfectly fine but then there is the very uncomfortable erratic beating going on near my rib cage.. What is this?