When laying flat on back I can feel a long hard mass about h i m seventeen and i noticed this yesterday while sitting in class. A small area where my rib cage is began to pulse. When i mean pulse, the first thing i noticed was how strong it was. no other area is doing it, that s why I am confused as to if it would be my heart beat. Since yesterday, it has not stopped. The pulse can be very very quick, like one after another and then stop completely and maybe pulse once on only 5 seconds. When I put my hand to it, it pushes my hand up. please help with some information! thankyou!