With young dogs and especially small one they don't have deep chests and there not chubby yet so it is not uncommon to be able to feel and see their heart.
To be able to know if there is a problem, a vet will need to listen to her heart. Sometimes there are murmurs present that can be felt as well.
If you just had her in and they say she is normal, than what you are seeing is normal.
Good Luck,
Dr.V
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Dr. D.A. Vamvakias
Veterinarian
