Six years after heart transplant, now-7-year-old Ava Martin is thriving -- and two families have an inseparable bond

HINSDALE, Ill. (CBS) -- We first told you about the story of the amazing Ava Martin six years ago.

In late 2015, Ava desperately needed a new heart – and she underwent a successful transplant. She received the heart of 2-year-old William Heard, who just had died tragically.

The transplant brought the two children's families together. CBS 2's Marissa Perlman checked in with both families Tuesday to see how they are giving back after loss, and how their once-in-a-lifetime friendship has thrived.

Ava is 7 now, and she's thriving herself. Perlman visited when she was posing for some photos.

"There's little glimpses of like, boy, you know, kind of tendencies or nature – just rambunctious," said her mother, Amie Martin. "She's just wild."

Amie Martin said her daughter's energy comes from a special place and person. That person is Willie Heard, whose heart lives on in her.

"I'm glad that I get to know who gave Ava that gift," Martin said.

CBS 2's Brad Edwards reported on the story back in 2015. At just 13 months old, Ava waited and waited for a new heart.

"Ava's fight to want to be here – that keeps you going, like, as a mother," Martin said.

That heart arrived just in time for Christmas 2015. In the operating room on Dec. 14, 2015, doctors told her new heart, "Welcome to your new home."

Across the country in Nashville, William's mother, Jamie Heard, had learned about Ava through CBS 2 reports a friend sent her.

William had been with his nanny eating chicken noodle soup when he choked on a piece of food, she says. Only at the hospital could doctors finally remove it, but by then the child did not have a pulse. A last round of medicine revived his heart, but the child did not show signs of brain activity.

Jamie Heard and her husband, Daniel, decided to donate his heart so that another child could be helped. He died Dec. 13, 2015 – the day before Ava underwent her transplant.

"I thought even if this isn't William's heart, I just wanted to pray for that mom, who received the greatest gift," Heard said.

But it was William's heart. And soon afterward, the families connected. Jamie Heard was able to meet Ava – and hear her son's heartbeat inside of her.

"It was a really healing time of light and hope when we were walking through a dark time," Heard said.

Now, Amie Martin and Jamie Heard are teaming up for a common goal – to put together care packages for families on the cardiac floor at Lurie Children's Hospital. It is a place the Martins know well.

"There were so many people that did that for us when we were there," Amie Martins said.

Organ donation has been healing for both families.

"His heart couldn't have gone to a better family," said Heard.

"They gave us the gift of more time with her," added Martin.

But beyond that gift, William's heart brought the families together. The Heards and Martins travel and celebrate holidays. Their four girls call each other "heart sisters" and Jamie Heard a "heart mom."

"It's not normal or typical for two families to want to connect as much as we have," Martin said.

Heard said the best part is watching Ava row up.

"She's so loving and endearing," Heard said. "I feel close to William when I'm around."

Heard is cofounder of  Faithfully Restored Women, a group that helps women going through a fought time. They will donate the care packages in time for Mother's Day and they will do the same at a Nashville hospital – the same one that treated William six years ago.