An 85-year-old man died while waiting in an accident and emergency unit because of "dangerous overcrowding", a hospital boss has said.
An email leaked from Northampton General Hospital NHS Trust to the Health Service Journal said the patient died after going to A&E with stomach pain on Wednesday afternoon.
He died after suffering a cardiac arrest early on Thursday morning.
The hospital said the long wait for treatment was "unacceptable".
The man was initially seen and assessed within an hour, and was waiting on a chair to be seen by senior staff after a blood test suggested he may have had heart problems.
But he deteriorated and suffered a cardiac arrest.
'Aware of risk'
The email from the trust's medical director, Matthew Metcalfe, said: "Last night a patient died due entirely to the dangerous overcrowding of the department.
"The risk we have all been aware of, but may have felt hypothetical, has just happened."
A spokeswoman for the hospital trust said the email was sent to all consultants "to ensure they were fully aware of the seriousness of the position in our emergency department and also the importance of their ongoing support to our patients attending the department".
"Ideally this patient would not have waited so long, would have been reviewed sooner by a senior consultant and might have been in a hospital bed on a ward at the time of his deterioration," the trust said in a statement.
"We don't yet know what difference this would have made to the final outcome."
The hospital's A&E unit has seen an average of 400 patients a day attending over the past few months, an increase of almost 30% on the same period last year.
The trust has apologised to the family of the man, and said it would carry out a full investigation into his death.