Why does my heart beat this hard and loud?

Why does my heart beat this hard and loud? I started some weeks ago, i used to feel like this once a week. But now it's like everyday, specially after I eat. For like a second, my heart beats so hard that I almost hear it. It's weird. And when it happens, I can't breath. It's not that fast heartbeat you get when you're nervous, it's different. It's like a full balloon ready to explode. I made every kind of things I should in the start of the year, because I was having panic attacks. Do I have a heart illness or is this just anxiety? And if it's an illness, could it be caused by anxiety?