A cardiologist at Wellington Hospital fears patients could die on waiting lists as surgeries are delayed.
The Cardiac Society is warning that patients needing urgent procedures were now waiting much longer as winter illness puts pressure on hospitals.
Some acute heart patients are waiting weeks in hospital for an operation, too sick to go home but unable to get a surgical slot.
Dr Scott Harding, who is also a spokesperson for the Cardiac Society, was concerned for patients in need of urgent procedures but who now face longer waits.
Cardiac surgeon fears deaths as operation delays continue
"This is not just a Wellington problem. It's a national problem at the moment. And again, it's hard to see that their problem is going to improve in the near future without a specific plan to address it."
He warned there could be serious consequences for patients left waiting.
"What we want to do is try and address this or have some mechanism for addressing it before, you know, people start having adverse events on the waiting list,"
"It [an adverse event] can be a heart attack, it can be death, it can be developing heart failure," Dr Harding said.
The Cancer Society was hearing about urgent procedures being cancelled too, typically at regional hospitals.
Cancer Society chief executive Lucy Elwood said "There are some on the day when it will just be that the nursing staff, or anaesthetist, or surgeon is now in isolation and there is actually no way for the hospital to then staff that surgery".
"That can be stressful for patients, especially if they have travelled for that surgery, they will have to travel back home and wait for another appointment," Elwood said.
For every surgery that is time critical, there are dozens of patients waiting for care that is classed as non-urgent.
Brain Tumour Support NZ said hundreds were experiencing delays accessing surgery and scans, with some unable to even set up appointments.
"People aren't actually getting answers from their doctors and can't even contact the neurosurgeon," chairman Chris Tse said.
MRI delays were the worst Tse had ever seen them.
"We have a lot of patients who are on active surveillance and they are meant to have regular MRI scans and if they are being delayed there is a risk that their treatment will be delayed," Tse said.
That includes Caitlin, which is not her real name. The 32-year-old had a brain tumour removed last year, but it was showing signs it was coming back.
"I have had quite severe migraines - so about four a week - and vomiting," she said.
However, Caitlin's MRI last month was cancelled and it could be four months or more before she could get one.
"You live with quite a bit of anxiety and you try to keep busy ... It does seem unfair," she said.
Te Whatu Ora, the new health authority, said it was monitoring the impact of the pressures on planned care and was working to ensure minimal impact on cardiac surgery.
It said decisions to defer cardiac surgery were made with clinical teams, and patient safety was carefully considered.
Te Whatu Ora was developing a plan to improve access to planned care services and reduce waiting lists, once the burden of Covid-19 on the health system starts to decrease.