2 heartbeats or yolk sac?

Leslie

Our surrogate had an ultrasound on Thursday, she was measuring 7 weeks, 2 days roughly. The tech said she saw the baby and heartbeat of 141, she then said she saw what might be a second heartbeat but then she said it could be the yolk sac?

Has anyone had something similar? I've never heard of this and after hours of googling it I still can't find an answer.

The ultrasound was not a diagnostic one, just one we paid for.