A shortage of staff to run heart-lung machines is causing problems at Royal University Hospital in Saskatoon—even leading to an open heart surgery operation being cancelled this week.

Cardiac surgeon Dr. Taras Mycyk told CBC News that perfusionists, who run the heart-lung machines, are becoming exhausted from overwork.

The Saskatoon Health Region has four perfusionists, but two are on leave.

That creates a problem, because a minimum of two well-rested perfusionists must be available when a heart bypass operation is performed, Mycyk said.

Before a non-urgent heart bypass this week, one of the perfusionists was clearly exhausted, he said. So, as a safety measure, Mycyk said, he cancelled the surgery.

Mycyk said it's not the first time he's cancelled a surgery because of overstrained resources, but it's the first time due to a shortage of perfusionists.

Documents obtained by CBC News concerning perfusionists in the Saskatoon Health Region reveal long-running tensions over workload and compensation.

The health region says it's bringing in some temporary backfill. Officials say the region has hired a fifth full-time perfusionist and hopes the two on leave can return soon.

On Friday, the union that represents perfusionists held a news conference to discuss the situation and said cardiac care is in crisis.

The Health Sciences Association of Saskatchewan says the provincial government has to act immediately to deal with critical shortages of health care professionals.

Perfusionists have been averaging 3,400 hours per year of being on call, and 300 hours of overtime in addition to almost 2,000 hours of regular work, HSAS said.

With the two perfusionists in Saskatoon who are on leave unable to come to work, the two remaining will either be working or on call all the time, the union said.