What Causes Faster And Harder Heartbeats With Slight Pain In 14 Year Old?

My 14 year old son has just woken up and come into my room saying when he awoke he felt no heartbeat. He moved around his bed trying to see if he could find it but still nothing. He could breath but felt nothing. He went to the loo and it started beating very slowly but irregular. He has just felt his pulse and says it was slower than once per second. I asked him to run around the house to see if we could raise it and make it a stronger beat as it is quiet. It beated faster but he had a slight pain in his heart when he started running and again when he came and lay back down and I was feeling it.