Jimmy Kimmel's Son's Heart Defect 'Has Been a Nightmare' for Him: 'They Know That Life Is Precious'

Jimmy Kimmel and his wife, Molly McNearney, have been riding an emotional rollercoaster since the birth of their son, Billy.

The 7-year-old was born with a rare congenital heart defect called tetralogy of Fallot (TOF) with pulmonary atresia and underwent his first surgery when he was only three days old.

"Billy’s heart defect has been a nightmare for Jimmy," a source spilled to a news outlet. "Jimmy’s been incredibly strong and hopeful, but also fearful."

Despite the worries and stress that comes with Billy's health problems, Kimmel and McNearney know that "life is precious" and "all that matters" to them is that their son is "okay."

As OK! previously reported, Billy just had his third open-heart surgery at Children's Hospital Los Angeles in late May.

"We went into this experience with a lot of optimism and nearly as much fear and came out with a new valve inside a happy, healthy kid," the 56-year-old late-night host wrote via social media after the successful procedure.

"Walking around this hospital, meeting parents at their most vulnerable, children in pain and the miracle workers who do everything in their considerable power to save them is a humbling experience," he continued. "And Billy, you are the toughest (and funniest) 7-year-old we know."

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During a recent appearance on Good Morning America, Billy's heart surgeon Dr. Vaughn A. Starnes explained that the little boy's condition totally took his parents "by surprise."

"They thought Billy was going to be perfectly normal and was until two or three hours after delivery," he shared. "That's when the nurse noted that the child was somewhat blue and sounded the alarms."

Dr. Starnes stated that Billy's condition was particularly a "very severe form" and described the situation as "the most scary, terrifying thing that a parent goes through."