Welcome, hendohbb! Yes, you have a cultured freshwater necklace, with very good luster. Yes, I've seen where mabe pearls are cultured in heart shape. But I can't tell from the photo if this is a cultured mabe or imitation. Are there karat gold markings inside or anywhere on the locket? On the bail? Can you see the back of the heart from inside the locket? If the locket is karat gold it should be marked somewhere.