Irregular heartbeat

I had a doctor appointment today and they sent me to labor and delivery because my baby had an irregular heartbeat on the doppler. I went to labor and delivery and they confirmed that it was irregular and I will need an ultrasound next week to look at her heart. They told me not to worry because they have seen this before and it typically corrects itself before the baby is born. I'm currently 27 weeks. Anyone experience this before? I'm trying not to worry but it's kind of hard not to.