irregular heartbeat @ 33 weeks

I'm currently 33 weeks pregnant, I went in for a check up the other day and when my doctor used the doppler I could tell that something was not right. she sent me to get an ultrasound, and after that I was hooked to a monitor for 30 minutes to graph the babies heart rate and beats. She said she was going to refure me to a specialist to get an echo cardiogram done on my babies heart. Has anyone else had an experience like this or know anything about it?! just trying to keep my mind at rest and not let myself become horribly stressed out... Thanks