(CBS) – In her 15 months on earth, this is the life that Ava Martin has come to know: more than two months on the 15th floor of Lurie Children’s Hospital, constantly hooked up to monitors and tubes.

She’s already endured two open heart surgeries, and is now in need of a heart transplant.

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Ava suffers from a rare condition known as hypoplastic left heart syndrome, which means the left side of the heart is severely underdeveloped. Amie and Brian Martin are Ava’s parents. One of them is with their daughter nearly every moment.

“Feisty is a good word to explain her,” Amie says.

Adds Brian: “She’s been through a lot, so she doesn’t put up with a lot anymore.”

She has been through a lot, seemingly one medical crisis after another.

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“She does have episodes of arrhythmia, where she goes into heart failure,” dad Brian says. “You’re always thinking about is she going to be here tomorrow?”

Such is life in the cardiac critical care unit at Lurie, where an average of 15 children receive transplants yearly. One child, Ireland, had just received a new heart, and Mia, like Ava, was waiting for one.

“The vast majority of patients who are listed for cardiac transplant ultimately undergo a successful transplant,” says Dr. John Costello, head of the unit. “The odds are in Ava’s favor. We just don’t know when we are going to get the call.”

And when they do get the call, the Martins know it will be one of the most cruel ironies of all: For Ava to live, somebody else’s child will not survive.

“It’s an intense emotion, and it’s hard to think we would be celebrating on a day someone else is going through such an awful day, because we may be faced with that day,” Amie Martin says.

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The Martins say family and friends have been their rock, even looking after older daughter Ella, who is 3. They have also set up a Facebook page and a Go Fund Me page to help with the family with their astronomical medical expenses.