(CNN) - Without a heart transplant, three-week-old Carter Cookson has just days to live.
The baby boy, from South Shields in the northeast of England, suffered three cardiac arrests after his birth on December 26, and a subsequent operation to fit a pacemaker revealed dead tissue in the left ventricle of his heart.
Parents Sarah and Chris Cookson have launched a social media campaign, #findaheartforcarter, in the hope of finding a donor for their son.
In 2013, they lost their first child, two-year-old Charlie, to a progressive disease doctors could not identify. The toddler couldn't breathe, eat, or sit up unassisted, and suffered frequent seizures. "It took five years after that for us to try again," Chris Cookson told CNN. "Now we're very much in the same situation again."
Carter is being treated at the Freeman Hospital in the English city of Newcastle, where an ECMO machine -- a life-support apparatus that performs the functions of the heart and lungs -- is keeping him alive. While doctors initially predicted the baby boy had five weeks to live in the absence of a transplant, issues with blood clots in the machine reduced his life expectancy further.
On January 16, his parents were told by the hospital that a donor needed to be found within three days.
"I'm praying that if somebody's in a very similar situation and is being told that their child is not going to live much longer, that they're willing to make that great sacrifice and donate the heart to let my boy survive," Chris Cookson told CNN in a telephone interview.
A spokesperson for the UK's National Health Service Blood and Transplant agency told CNN in an email that a total of eight babies under the age of two in the UK are in need of a heart transplant. For patients under 18, the average waiting time for a donor heart currently stands at 70 days for those on the NHS' "urgent list," or 463 days for cases considered non-urgent.
"Children waiting for an urgent heart will wait two and a half times as long as adults waiting on the urgent list," the spokesperson said.
Donor hearts typically come from within the UK, though they are sometimes obtained from countries in Western Europe, according to the British Heart Foundation.
Despite the bleak prognosis, Cookson said he and his wife would "fight to the last minute to get Carter a heart." He hopes, too, that Carter's story will encourage others to join the organ donor register -- and support the UK government's plans to move to an "opt-out" organ and tissue donation system in England.
In August 2018, the government said the new system, which would see people automatically assumed as willing to donate their organs unless otherwise stated, could be in place in England by spring 2020. Wales has operated an "opt-out system" since 2015 and the Scottish government has published a parliamentary bill that, if passed, would also create this arrangement.
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