Rebecca Voltmer watches her classmates run through a dress rehearsal of You Can't Take It With You, the 1937 Pulitzer Prize-winning comedy.

It's hell week - theater-speak for the days before opening night - and the Abington Senior High School cast is amped.

Rebecca stands a curtain fold from being on stage, blond hair sliding over her shoulders, arms hugging her gray sweatshirt, smiling at a funny line. And then longing captures her face. She so wants to be out there, bathed in the footlights, exchanging lines with the other actors.

And she would be, if only.

Rebecca, now 17, missed the show's June auditions because she was home in bed, two ventricular assist devices (VADs) whirring in her chest, waiting for a heart transplant.

The number of American children with heart failure and who need a transplant is growing. Exact numbers are hard to come by, but Joseph Rossano, a pediatric cardiologist at Children's Hospital of Philadelphia, estimates that 14,000 to 16,000 children yearly are admitted to hospitals in the U.S. with heart failure.

"We have a growing heart-failure population," he says.

The largest group is children born with severe congenital heart defects. There are also children with cardiomyopathy (heart muscle disease), some of whom can be managed with medication. But others eventually will need a heart transplant.

And then there are children who are completely healthy with no history of heart disease who get sick out of the blue with a severe heart infection and inflammation, called myocarditis. Rebecca is among them.

"The vast majority of these types of infections are viruses," Rossano says. "They tend to be common viruses, things that we're exposed to all the time."

Last spring Rebecca was a vibrant, outgoing young woman who liked hanging out with friends, going to concerts, and bugging her younger sister Paige, 15, and little brother Egon, 9. But acting, singing, and dancing is what she really "loves to do."

"I'd be a table," she says looking at the props on stage during the rehearsal. "I love being on stage."

It wasn't long after the school's spring production closed last year that Rebecca started feeling weak, tired, and short of breath. In early April her parents, Joan, 45, a nurse at Fox Chase Cancer Center, and Egon, 52, chef at the Dreshertown Shop-N-Bag, took her to the emergency room of a local hospital. Rebecca, they were told, was dehydrated. Two liters of intravenous fluid later, she was sent home.

Three days later she was back, feeling worse. This time doctors told her parents that she was depressed and seeking attention. The family went home to Glenside. Over the course of days, Rebecca continued sliding downhill. A walk around the block ended with Joan calling Egon to pick them up.

Late one night Egon saw Rebecca sitting up in bed staring at the wall. When he asked what she was doing, Rebecca said it was easier to breathe.

"Everybody else was asleep," Egon says. "So she wasn't looking for attention."

Joan got a referral to Zev Jacobson, an Elkins Park cardiologist. After an echocardiogram and EKG, Jacobson laid his stethoscope on Rebecca's chest.

"He listened to my heart for a few seconds and gasped," Rebecca says.

Joan asked if her daughter was in heart failure and "he said yes." Rebecca's heart was pumping at 10 percent. Jacobson said the family had to go immediately to Children's, by ambulance. Egon followed in his car. From the ambulance Rebecca could see her father and asked her mother why he was crying.

"I was really scared and saying my prayers," Egon says. "And then the Beatles song "Let It Be" came on the radio. I just remember how comforting that song was, you know, let it be and things will be all right."

When Rebecca got to Children's, a team of doctors and nurses, looking "scary" - dressed in gowns, gloves, and masks - descended on her as if she were being "swarmed by bees." The doctors told Joan and Egon that their "daughter is very sick."

Days turned into weeks and weeks dissolved into months. The doctors tried to coax Rebecca's heart to recover with medication. She didn't respond. They placed her on a ventilator and an extracorporeal membrane oxygenation machine (ECMO) to give the muscle a rest. ECMO, says Rossano, is a rescue therapy used in the intensive care unit to keep people alive for a few days. Rebecca would be on it for 17 days.

On Mother's Day, an ECMO tube dislodged. Rebecca hemorrhaged and needed emergency surgery. ECMO was over. The next step was inserting a VAD in Rebecca's chest. Joan and Egon had to sign for the surgery. They also signed the paperwork to place Rebecca on the heart transplant list.

Rebecca went into surgery expecting to have one VAD implanted. The mechanical pump is small enough to fit in the palm of your hand. It is placed inside the body. Only the wires for the power source are visible. The wires attach to a battery carried in a fanny pack around the waist.

But Rebecca's right ventricle, which pumps blood to the lungs, wasn't working. She needed two VADs.

"Thank God we have CHOP," Joan says. "They always had a plan to get her better. They anticipated her getting bad and always had a plan."

Rebecca went home with her VADs on June 28 to wait for a heart. She spent five weeks in bed. One evening Egon was trying to get an Amazon gift card to work online. About 7:30 the phone rang. It was the transplant team. They had a heart.

"We were watching a YouTube video and cracking up when my dad came in and said, 'We need to go. We have a heart,' " Paige says.

By 9 p.m. the family, minus little Egon, was at the hospital. They entered the transplant floor to cheers from the staff. Rebecca went into surgery about 5 a.m. On July 28, at 11:14 a.m., Rebecca's new heart beat for the first time. She considers it her second birthday.

"That's exactly what it is," Rebecca says. "You have a regular birthday and a heart birthday."

Less than two weeks later, she was home. She returned to school on Oct. 20. Rebecca is on two anti-rejection drugs, plus steroids and blood pressure medication.

She has been overwhelmed by the outpouring of support her family has received from family, friends, and neighbors, from supplying dinners and walking the dog to groups praying for her as far away as France and Germany.

Rebecca plans to write a letter to thank the donor's family. She wants them to know how grateful she is for her second chance and that she will take care of their gift to her.

"I never say that it's my heart," she says. "I'm just taking care of it for an old friend."