To see 8-year-olds Siobhan and Michelle dancing in their Valentine's Day outfits, you'd never know that they underwent open heart surgeries before they could walk.
Interested in ?Add as an interest to stay up to date on the latest news, video, and analysis from ABC News.
For them, visits to the hospital aren't so scary. That's because the girls -- and their families -- have always had each other.
"We were just all in this together," said Louise Bogue, Siobhan's mother, adding that she would often call Michelle's mother, Elizabeth Mancini, to talk about oxygen levels, medicine, and when to go to the emergency room. "It's nice to be able to share the language."
Bogue and Mancini were best friends at St. Joseph's College in Brooklyn, and today live just six blocks from one another. Bogue's daughter Siobhan was born first, in June 2006, with a congenital heart defect. The tiny baby was missing one of two valves to connect the top and bottom chambers of her heart, and there was a hole between those chambers. She had her first surgery in August of that year and but was too small for the open heart surgery to add another valve, which she couldn't have until she reached 12 pounds in November.
Mancini, who was pregnant with Michelle at this point, was Siobhan's godmother.
"When Siobhan was going through this, when she was first born, there were a lot of touch and go days," Mancini said. "I sat there thinking, 'I don't know how Louise does this.'"
Michelle was born a few months later in December. About a month later, she spent a week in intensive care with what looked like pneumonia, and doctors thought they heard a heart murmur. Michelle was soon also diagnosed with a congenital heart defect. There was a hole between the upper and lower chambers of her heart, too.
In disbelief, Mancini called Bogue as she left the cardiology unit, and Bogue gave her the phone number for Siobhan's doctor at Mount Sinai Hospital in Manhattan. There, Michelle underwent a surgery to fix a valve and repair the hole in her heart without having her chest cracked open, Mancini said. Doctors went in through Michelle's armpit.
"It hit me when I found out about Michelle," Mancini said. "Alright, she went through this, so I can go through this."
At one point, Michelle needed to be hooked up to an oxygen tank at home, scaring Mancini's older daughter because her grandmother had died shortly after needing a similar tank.
"That was kind of like death in her head," Manicini said. But seeing that Siobhan had an oxygen tank sometimes, too, made it less frightening, she said.
Siobhan, who has Down syndrome, had to undergo four surgeries the year she turned 4 and several other procedures over the years to widen her tricuspid valve, Bogue said. Her most recent procedure was in August, and she'll probably need two more surgeries in her lifetime, said her pediatric cardiologist at the Kravis Children’s Hospital at Mount Sinai, Dr. Shubhika Srivastava.
Michelle underwent one more procedure, and both girls go to Mount Sinai for regular scans and checkups. They call each other "frousins," meaning friends who are like cousins.
But on Wednesday, the girls were back at the hospital for a happy reason: the Valentine's Day reunion.
"When they go to Sinai for heart parties, they feel like complete rock stars," Bogue said, adding that Siobhan likes to wear her red party dress and heels.
Srivastava said the girls are "the life of the party." And it's clear to her that the families have gotten strength from one another throughout their ordeals.
Knowing that Siobhan has right-sided heart failure, Srivastava said she loves to see her act like a normal kid with Michelle.
"When I see her dancing and enjoying life, it's so rewarding," she said.