Kimmel posted the photo this afternoon of his wife, Molly McNearney, holding their son while big sister Jane "listens" to his heart with her toy stethoscope.
"Sincere thanks for the outpouring of love & support - Dr. Jane is keeping a close ear on Billy, who is very well," the late-night host wrote on Twitter.
Earlier, McNearney tweeted a photo of her husband cradling their son's head. "I am thankful to love and be loved by these two brave guys. Both criers," she wrote.
On Monday's "Jimmy Kimmel Live" Kimmel revealed that his son had emergency surgery last Monday, three days after he was born, after doctors discovered he had a heart defect. Luckily, he said, the operation was a success, though his son will need to undergo a second open-heart procedure within the next three to six months.
Kimmel also urged viewers to donate to Children’s Hospital Los Angeles, where his son's surgery took place, and made a plea for politicians, both Republican and Democrat, to make sure all Americans have access to medical care, especially those with pre-existing health conditions.
"Well said, Jimmy. That's exactly why we fought so hard for the ACA, and why we need to protect it for kids like Billy. And congratulations!" Obama wrote.
McNearney retweeted the former president, adding, "Someone is angling to be Billy's godfather."