Father-of-two Gareth Evans has needed a heart transplant for nine years.
The 45-year-old, from Stockport, has been waiting longer than anyone else in the UK on the current list of heart transplant patients.
His health is declining and, as Organ Donation Week begins, the NHS wants people to join the UK's donor register.
NHS Blood and Transplant figures show about 3,000 lifesaving transplants were missed in the last year, as families would not donate relatives' organs.
They also show 80% of people support organ donation, yet only 33% of people have told their family they want to donate.
Gareth originally had a heart transplant in 1990, aged only 17, after he contracted cardiomyopathy, a disease of the heart muscle.
The heart has lasted 28 years, which is long for a donor organ, but now it is failing.
He has spent the last three months in Wythenshawe Hospital, Manchester, where he is having IV medication to correct the damage done to his organs as his heart deteriorates.
"I never thought it would take this long to find a donor," he said.
"I feel like I'm merely existing, not living. It was a lot easier to get through it as a 17-year old lad. Now I have the most awesome wife and kids that I worry about and I get very emotional when I think about them.
"Having to tell the family you might not make it is the most difficult thing to do," added Gareth, who is married to Danielle and has two sons aged 10 and 13.
Anthony Clarkson, interim director of Organ Donation and Transplantation at NHS Blood and Transplant, said the issue was often that family members had not communicated their decision on organ donation.
"Families tell us that they don't know their relative wanted to be an organ donor, and therefore they err on the side of caution and say no.
"Then often their family member becomes too ill to have the conversation and it is too late."
There are currently 6,133 people on the transplant waiting list and in the UK in 2017, 411 people died before the right donor was found.
NHS Blood and Transplant is urging people to sign up to its Organ Donor Register, and to tell their families their wishes.
Organ Donation Week will be be marked by councils, businesses and hospitals lighting their buildings pink.
The campaign comes as the government has announced that it aims to introduce a new "opt-out" law in England, which will assume that over-18s are in favour of donating their organs when they die, unless they specifically register to "opt out."
If voted through in the autumn it will come into effect in England from spring 2020.
The government said this could save up to 700 lives a year.
A similar opt-out system has been in place in Wales since 2015. Scotland plans to introduce a similar scheme and Northern Ireland has also expressed an interest.
Mr Clarkson added: "We know that organ legislation will change, but the harsh fact is people are dying right now waiting for an organ, so it is important to share your wishes now."