J.H.
Where do you live? Who did the ultrasound? A regular OB or a perinatalogist (specialist with better machines and additional expertise)?
If you wanted to take a closer look, then I would request a referral to a pediatric cardiologist for a fetal echocardiogram. I work at Texas Children's in Houston. Here, Dr. Nancy Ayres is very highly regarded as an expert in this field. The perinatalogist that I saw here in Houston was Dr. Brian Kirshon. He is also excellent!
Let me know if you need additional information. I can send the phone numbers for these folks. If it would give you peace of mind, you could pursue either or both of these options.