What Causes Sudden Fluttering Of Heart?

Hi First let me say that I have been to the cardiologist on very occassions and the last time I went (my regular physican recommended a follow-up visit because I hadn t been in a while and supposedly I have what they call a bicuspid valve. So I went and he told me that my heart apppeared to be functioning properly. My concern that I shared with him was that every once in a while all of a sudden my heart starts like flutterly pretty strongly and will go on for a few minutes I get very weak and my arms seem very heavy when this occurs. My visit was just before my daughters wedding (as he suggested just to be sure all is ok, that I could go for a stress test and also possibly wear a monitor) I advised it would probably be after wedding and he indicated there was no urgency. Well I hadn t had any symptoms of this for the last 3 months or more so of course I didn t go and then all of a sudden I had this occurrence. I m a thin person and when this is happening I feel like my whole upper body is moving. Any thoughts?