A human heart will beat about 3 billion times in a lifetime. It's an amazingly durable and hardworking organ. But only if it's healthy. My assistant, Julia Feldmeier, has the story of a tiny heart that wasn't. Thanks to the doctors at Children's Hospital, it is now.

When you are an expectant parent, said Matt Campbell, you expect that your baby will be perfect. Healthy and gurgling, with 10 fingers and 10 tiny toes.

Matt and his wife, Jennifer, of Leonardtown, certainly expected as much a year and a half ago, when they found out that Jennifer was pregnant with a second child. Their daughter, Erin, now 21/2, had been "perfect," and it seemed natural that Sean, the new baby boy, would be perfect, too, said Matt, 36. "It's the default assumption: Everything's going to go perfectly."

So when a 20-week ultrasound revealed that Sean's heart was dangerously imperfect -- essentially, that the left half of his heart was missing -- "my own heart just kind of stopped for a minute," said Jennifer, 37.

Sean's condition is known as hypoplastic left-heart syndrome, a rare defect in which the left ventricle, the heart's main pumping chamber, is grossly underdeveloped and useless. Without treatment, 95 percent of babies with HLHS die within the first month of life. But with a three-pronged series of operations, surgeons can rebuild the heart so that the right side pumps blood to the body. Typically, the first operation takes place 48 hours after birth.

But Sean couldn't hold out that long, doctors determined.

Not only was the left side of his heart underdeveloped, but his atrial septum -- the hole that allows oxygen-rich blood returning from the lungs to drain from one upper chamber to the next -- was closed.

"Babies who are born with this combination are delivered and decompensate immediately," said Dr. Mary Donofrio, the director of the fetal heart program at Children's Hospital who discovered Sean's sealed atrial septum last December, a month before Jennifer was due to deliver. "They really have no blood flow to their body because there's no way for the blood to get out of their lungs."

Roughly 70 percent of babies with this combination die, according to Donofrio.

For Sean to survive, he would have to be born at Children's -- there wouldn't be time to transport him from Washington Hospital Center, where Jennifer had initially planned to deliver. This in itself was a risky maneuver: Sean would be only the second baby ever to be born at Children's.

Donofrio coordinated a team of Washington Hospital Center doctors to come deliver Sean. On Jan. 18, Sean was born via Caesarean section, weighing 6.5 pounds, and was immediately whisked to the catheterization lab. There, Dr. Richard Jonas, chief of cardiovascular surgery at Children's, inserted a catheter into Sean's leg and navigated it up to his heart. Attached to the catheter was a small blade, which Jonas used to puncture the atrial septum, and a tiny balloon, which he pulled through the puncture to widen the hole.

All this on a heart the size of a grape.

It was the first time this particular catheter had been used on a baby with HLHS, Donofrio said, and "it allowed us to save Sean's life and make him well enough so that he could go to the operating room. It's a very risky thing to go straight from the delivery room to the operating room because you need to give the baby a chance to get used to the outside world."

Two days later, Sean had the first of the three surgeries he'll need to ensure a properly functioning heart. Jonas placed a small tube in Sean's heart, restructuring the blood flow so that it bypassed the left ventricle and enabling the right ventricle to pump blood to both the lungs and the body. In June, Sean had his second operation, which reduced strain on the right ventricle by diverting half of the deoxygenated blood directly to the lungs. The procedure was equally successful.

He'll undergo the third -- and hopefully final -- surgery in late spring, routing the remaining deoxygenated blood directly to his lungs and thereby ensuring that oxygenated blood and deoxygenated blood don't mix in his heart.

Save for a tiny scar on his chest where a pendant necklace might hit -- Jennifer calls it his "badge of courage" -- Sean shows no signs of his battle.

At 20 pounds, cheeks chubby and eyes sparkling, the 10-month-old is happy and healthy. And picture-perfect.

The Beat Goes On

The Campbells were lucky. Their health insurance covered most of the cost of Sean's life-saving treatment. But even if it hadn't, the sick baby wouldn't have been turned away.

That's because of readers such as you. You can do your part to help ensure that all kids get the best treatment available by taking part in our annual fundraising campaign.

Our goal by Jan. 20: $600,000.

Our total so far: $7,306.31.

There are three easy ways to make your tax-deductible donation:

Make a check or money order payable to "Children's Hospital" and mail it to Washington Post Campaign, P.O. Box 17390, Baltimore, Md. 21297-1390.

Go online, to www.washingtonpost.com/childrenshospital, and click on "Make a Donation."

To contribute by Visa or MasterCard by phone, call 202-334-5100 and follow the instructions on the recorded message.

To see Sean's photo, go to www.washingtonpost.com/johnkelly.