Why can I sometimes hear my heartbeat in my head and sometimes I can't?

Its a mystery! We don't know why...but we physicians hear of this frequently. To even hear your own heart beat ever is a bit odd, you must admit. The term given this is cardiac awareness. We believe sometimes its presence is due to how one lies in bed on one ear, hence facilitating auscultation. Why it is not always apparent at other times is unanswerable. The whole condition is felt a normal variant.