The 45-year-old teacher's irregular heartbeat had been playing up for days and she was starting to feel dizzy, nauseous and lethargic.

"I called Nurse-on-Call and they were very clear… they said you need to get to hospital within the next 45 minutes and if you can't get there, call an ambulance. It was pretty scary," she says.

Ms McIver's husband drove her to Monash Medical Centre's emergency department in Clayton. When she arrived, it was packed. She joined a standing queue of six people waiting to see the triage nurse.

About 20 minutes later, the nurse took her history, checked her heart rate and measured oxygen in her blood. She was told to sit down and wait.

Ms McIver says the nurse gave her no indication of how long she would wait. So she sat and waited, and felt increasingly anxious about what was happening to her.

As her heart beat continued to fluctuate over the next two hours, the mother-of-two's instinct told her she couldn't wait. She called a private hospital nearby. It had no waiting list, so she and her husband left.

"I was feeling pretty rotten," she says. "I went over to an admin person and I said 'I'm going', and he just said 'Ok'... That was it."

Ms McIver is one of thousands of patients who left a public hospital emergency department without treatment this year.

Dr Simon Judkins, from the Australasian College for Emergency Medicine, said Australian Institute of Health and Welfare data showed four per cent of patients who arrive at emergency departments leave before they receive treatment for their condition, usually because they waited too long on busy days.

He said Ms McIver was probably a category-three patient on the triage scale who should be seen by a doctor within 30 minutes. This category includes women having miscarriages, people with painful fractured hips, and those with mental health conditions who are not saying they are suicidal.

Dr Judkins said people in this group often wait for hours when emergency departments get overwhelmed and critically ill people are prioritised. The category-three patients can be dangerous, he said, because some deteriorate in the waiting room.

"There's always potential for them to have something more serious that's been missed," said the doctor who is calling for more resources for Victorian hospitals.

Ms McIver went to The Valley Private Hospital in Mulgrave where she said she was admitted within 5 minutes to receive tests and treatment for her heart condition. She was OK, but it cost her about $400 to find out. She's still angry about how unsafe she felt in the public system, and the fact that some people could not afford to make the choice she made.

"I was so angry that my bank account dictated my care. It's so wrong. If you're sick and you're afraid, you need to be taken care of," she said.

"The staff [t Monash] were doing everything they could but they just didn't have the resources to do a proper job."

A spokesperson for Monash Medical Centre said its emergency department was one of the busiest in Australia and that it faced high demand in August and September due to flu season.

"We strive to provide timely care for all patients. However, during periods of high demand we prioritise care according to clinical need," she said.