Most fathers and daughters share very close bonds, and some of them even share rituals that symbolize their love for each other. Josh Trimble and his six month-old daughter Opal share one of these rituals, as they rarely leave one another without pounding their chests as if they are “sharing a heartbeat.”

Opal sadly suffers from a rare polio-like disease called acute flaccid myelitis (AFM), which affects the nervous system and causes weakness in the arms and legs. As she battles the rare illness, Opal has been hospitalized at Children’s Center Rehabilitation Hospital in Bethany, Oklahoma for the past few months.

Last month, a video went viral showing Josh and Opal’s heartwarming goodbye ritual after it was shared to Facebook by the Oklahoma Blood Institute. In the video, Josh can be seen pounding his chest as Opal mimics the gesture back to him.

“Just look at this sweet video of Opal Rose, a blood recipient, and her daddy,” the institute captioned the video. “Opal is recovering from acute flaccid myelitis (AFM), a rare illness that affects children. Dad, Josh, tells us this is his way of showing Opal he’s always with her and there for her, and that they share a heartbeat.”

“That moment of me beating on my chest was actually Opal and I sharing a heartbeat,” Josh added. “I was letting her know that even though we may not be there physically together, we share a heartbeat.”

Opal was just four months-old when this video was shot, and she had been immobile for several weeks recovering.

“We had just finished some hard days of physical therapy for Opal, and her physical therapist had been trying to get her to reach out for things,” Gretchen Trimble, Josh’s wife and Opal’s mom, said of the day the video was captured. “We were just so encouraged because the fact that she was mimicking him told us she knew what she wanted to do and she did it.”

Gretchen recently said that Opal’s condition has improved since the video was taken.

“The past few days have such good days for Opal Rose,” Gretchen said. “It’s just so incredibly good to see her normal, happy self.”

Check out the video for yourself below!