The 70-year-old, believed to be from Paynesville, was transferred by ambulance to Bairnsdale Regional Health Service in the state's east on Monday.
With no beds free, the man remained in the care of paramedics on a stretcher inside the hospital for about three and a half hours before he went into cardiac arrest and died.
Bairnsdale Regional Health Service and Ambulance Victoria have launched an investigation.
"We will work with the hospital to fully review the circumstances of this case," an Ambulance Victoria spokesman said.
Victorian Ambulance Union General Secretary Danny Hill said four or five crews were ramped at the hospital on Monday, including the patient who died.
"The emergency department was completely overwhelmed. A lot of patients were unable to be moved up to wards because they were full," he told AAP on Wednesday.
A three- to four-hour wait for hospital treatment is not unusual for some Melbourne hospitals but less common in the regions, Mr Hill said.
It is the latest episode linked to Victoria's under-pressure health system, with at least 12 people dying since October after calls for an ambulance to the state's triple-zero service went unanswered or weren't picked up quickly enough.
Mr Hill said the COVID-19 pandemic has exacerbated, not created, problems within the health system, and the lack of alternative services in the bush often makes residents feel like their only option is to call triple zero.
"The system seems to focus on the only two options which is ambulance and emergency department," he said.
"Opening up access and improving access to 24-hour GPs, aged care in-reach - all those sorts of things - is really where the attention should be focused. Not just on putting on more ambulances and more ED beds."
A Victorian government spokesman offered his condolences to the man's family and friends and confirmed an investigation was under way.
"It would be inappropriate to comment while those investigations are taking place," the spokesman said in a statement.
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