The Minister of State for Health has promised improvements after a pensioner's life-threatening condition was not identified because emergency staff at Tameside Hospital were so busy.
Seventy three-year-old John Turner died at the Ashton hospital on August 23 last year.
he had previously attended the department three days before, but his condition was not identified.
An inquest in June found Mr Turner's death was the result of a pulmonary embolism and deep vein thrombosis.
However, area coroner Chris Morris issued a prevention of future deaths report after hearing Mr Turner had been left waiting in A&E because staff were busy.
Evidence was also given revealing it was almost eight hours before the doctor who reviewed Mr Turners condition was able to record her findings on the hospital's computer system. Mr Morris said the delay "in all likelihood reflected competing clinical demands on her time".
He said: "I am concerned, as a practical consequence of unremitting demand on this and other emergency departments, the scope for identifying major or life-threatening illnesses which presents atypically is significantly reduced."
Mr Turner fell ill while holidaying in Greece. He had a cough and on returning home, became more and more breathless.
He was diagnosed antibiotics by his GP but his symptoms did not improve. He went to Tameside Hospital where he was assessed, but was sent home without further treatment and a blood test to identify blood tests requested by the triage nurse was not carried out.
Mr Morris added: "The court heard evidence as to a wide range of factors ranging from demographics, difficulties in accessing primary care and increasing acuity of illness in an ageing population which have combined to create great pressure on hospital emergency department."
The coroner demanded answers from health minister Karin Smyth to help prevent similar deaths in the future.
Ms Smyth. replied in a letter to the coroner: "The report raises concerns regarding poor patient flow and delays to patient care due to competing clinical demands, particularly during times of high demand at Tameside and Glossop Integrated Care NHS Foundation Trust (TGHT).
"Patient flow is a significant issue facing hospitals across the country which can lead to unacceptable delays for patients.
"I am informed that Mr Turner was triaged as a category 2 (to be seen by a clinician within 120 minutes) and was seen at three hours, 13 minutes post triage due to the pressures in the emergency department on that day.
"I understand that TGHT has recently opened the rebuilt emergency department, which now has a larger footprint and the capacity to see more patients simultaneously. This is expected to improve waiting areas and reduce waiting times for patients.
"At a national level, this government is committed to returning to the safe operational waiting time standards set out in the NHS constitution."