An emotional video has emerged from the US of the mother of a heart donor hearing her late son's heart beat inside the chest of the man who received it.

In the clip, which was filmed on May 21 in Roanoke Rapids, NC, the woman listens to her son's heart using a stethoscope.

It's clearly an emotional moment and as the mum starts to well up she gives the recipient of the heart a big hug.

The man in the video, Greg Robbins, had his heart transplant in September last year, shortly after the 31-year-old donor died in a car accident.

''Six months after the transplant, we got the letter from the donor's mother. We met the family in May 2017 and it was awesome, as you can tell from the video,'' the filmer later wrote online.

''Greg Ricks (the donor) was divorced so his mother is the one who made the donor decision. At first she said no to the doctors when they asked about donating his organs but after a few minutes changed her mind and said yes.''

''If she had not changed her mind, my husband probably wouldn't be alive today because he only had a few weeks to live. Greg Ricks and his mother, Anna, are my heroes,'' she added.