TORONTO - A baby whose health was so poor her parents offered her heart for transplant before she managed to pull through is back on life support in hospital.

Kaylee Vitelli returned to Toronto's Hospital for Sick Children early Thursday after her family said she stopped breathing and they couldn't revive her, a family spokesman said.

"She had stopped breathing (Thursday morning) more than usual," said JP Pampena, regarding the girl who suffers a rare condition where halted breathing is common.

"(Her) dad figures she either had a stroke or a heart attack but that's unconfirmed, they're still waiting for results from tests they're taking."

Around 2 a.m. Thursday paramedics rushed Kaylee by police escort to Southlake Regional Health Centre in Newmarket, Ont., just south of her home in Bradford, before she was immediately transported to Toronto.

The four-month-old suffers from Joubert syndrome, a malformation of the brain and brain stem accompanied by frequently interrupted breathing.

The family reports that doctors have told them she's now in critical but stable condition, Pampena said. It's anticipated she'll remain in hospital for a lengthy period of time.

Doctors have also cautioned the family that if she is able to return home, the infant will still require life support, he added.

Kaylee's heart was offered to another infant when her parents thought she would die in April, but she returned home the following month after she rallied.

Kaylee last returned to Sick Kids in late May, when she was diagnosed with a skin infection that had travelled internally. However, she once again was released to her family's home about 60 kilometres north of Toronto.

The girl's parents are asking the media for privacy.