Joe Kelly, 65, was told twice the operation was being called off because of a shortage of intensive care beds at Wythenshawe Hospital, Manchester.
He died at his home two days before he was due to go into hospital for a third time.
A hospital spokeswoman said last night: "The incident is being investigated fully. We made every effort to get Mr Kelly into Wythenshawe at the earliest opportunity. It was a clinical judgement that he be discharged on 15 December because of lack of available intensive care beds.
"The hospital was under particular pressure before Christmas. The intensive care unit was full of sick patients who could not be moved."
Mr Kelly was admitted to hospital on 15 December after an earlier operation was cancelled. "Joe even had a body shave for the operation," said his widow, Pauline, of Chorlton cum Hardy, Manchester.
"Then they said they were sending him home and he should come back again for the operation on December 19," she said. Mr Kelly died early on 17 December.
The hospital spokeswoman added that it was treating an increasing number of heart patients: "Last year we treated 200 more cardiac surgery patients than the previous year."Reuse content