How long until a transplanted heart loses its original cells and become part of the new body?

It doesn’t ever become part of the new body.

Transplanted organs renew via mitosis of the donor’s cells, and retain their own DNA. The recipient must remain on anti-rejection medication for the rest of their lives.

Normally cells get completely replaced in 11 months. Transplanted cells get replaced by the same transplanted cells. You would need a lot of stem cells for a total replenishment of native cells.

Oh, thank you for the information. I am beginning to remember how cells divide. It’s been a long time since I read up on that.

Whose heart it is depends on how you want to define it.

Regardless, there is the connection. The recipient and their family can always feel grateful to the donor’s family (and donor in a living donation) for the life-saving gift.

In the case of the bride, her dad’s been gone ten years but he had an active involvement in the wedding. By checking the “donor” box, he helped the other guy live to see the day.