ST. PETERSBURG, Fla. -

Gavin was the best big brother 4-month-old Mia could want - but not because he’ll one day help her with homework or give her advice about boys. In fact, she’ll never meet him.

Gavin was stillborn in September 2012, 29 weeks into Priscilla Cervoni’s pregnancy. An autopsy revealed he suffered from dilated cardiomyopathy, a condition that causes the heart to weaken and enlarge.

Nearly a year later, Cervoni was 29 weeks pregnant with Mia when she went in for an ultrasound. Keenly aware of Gavin’s fate and the tendency for cardiomyopathy to be genetic, Cervoni’s doctors had been watching the pregnancy closely. During the ultrasound, the technician asked the doctor to look at something on the black-and-white screen.

“The tech said ‘come here’ and the instant she said it, I knew. I looked at my husband and I started crying,” said Cervoni, 34, of Clearwater. “I thought, ‘Oh no, I cannot go through this again, I cannot bury another child.’ “

Mia’s heart looked “thick” on the ultrasound. Doctors confirmed that like Gavin, she had dilated cardiomyopathy. Mia was given drugs in utero to regulate her heartbeat and help her survive the pregnancy.

She responded so well to the drugs that doctors let the newborn go home, hoping her condition would improve. Six weeks later, though, she was admitted to All Children's Hospital in St. Petersburg, where she’s been ever since. At only 4 months old, Mia needs a new heart.

Cardiomyopathy is a general term that describes weakening of the heart caused by the muscle becoming large, thick or rigid. Dilated cardiomyopathy, said Dr. Alfred Asante-Korang, Mia’s cardiologist, is when one of the ventricles - the left, in Mia’s case - becomes enlarged. Mia’s heart is two and a half times bigger than it should be - the size of a healthy 6-year-old’s.

The condition is rare: Asante-Korang said about one out of every 1,000 babies is born with it. It can be genetic or caused by an infection.

Cervoni and her husband, Kevin, underwent testing to determine whether they carry a genetic abnormality that could cause the condition. The tests came back negative, but Asante-Korang isn’t convinced. Doctors have identified about 90 genes associated with the problem, but more may yet be discovered.

“I think it’s genetic,” the doctor said. “Look at how uncommon the condition is, and to have two babies with the condition, usually that’s genetic. We just don’t know the gene yet.”

Mia’s big brown eyes are what people notice first. She’s very expressive with her eyes, her mother said, because all Mia can see of other people is their eyes above the masks they must wear to protect her from germs.

Mia has an older sister, Kylie, 5, who is healthy and excited about having a sibling in the family.

“She’s been waiting to be a big sister for a long time,” Cervoni said. “She was very excited about having her brother, and he didn’t come home.”

Kylie plays with Mia in the hospital room, jumping around while Mia laughs. They watch TV together.

“Kylie totally gets that Mia needs a new heart,” Cervoni said. “She knows that Mia’s heart is broken and that she needs a new one so that she doesn’t have to go to heaven.”

Cervoni lives a split existence - with Mia at the hospital during the day, with Kylie at home at night. She’s on leave from her job in billing at a medical consulting company until she can return. But her husband was furloughed from railroad giant CSX in December, just two weeks before Mia was placed on the transplant list.

The family receives health insurance through CSX for now and will be covered under the Affordable Care Act, sometimes called Obamacare, when CSX’s coverage expires. The family also will be eligible for Medicaid to help pay for the operation.

However, the insurance can do little to defray the secondary costs of the surgery, such as lost income and a lifetime of doctor copays and drugs for Mia.

Kevin picked up some shifts at Home Depot to help, but the family also started a donation fund with a nonprofit based in Indiana, the Children’s Organ Transplant Association.

Donation checks can be made out to COTA, with “In honor of Team Mia C” in the memo line, and mailed to the association at 2501 W COTA Drive, Bloomington, Ind., 47403. Or visit the website COTAforTeamMiaC.com.