At an inquest this week Coroner Alan Craze said medical staff could not have realised symptoms displayed indicated the rare heart disease which affects two - three people per 100,000.
But he questioned the actions of a Sister who refused to admit him to the cardio care unit despite a request from a junior doctor who was concerned about his condition.
And he also queried why no heart scan equipment was available when requested.
Stephen Hemsley, a care worker of, Laton Road, Hastings, was first admitted to the Conquest on July 2 2012 after suffering from diarrhoea and abdominal cramps for two weeks. He was kept in for tests and observation overnight but discharged the next day.
He was readmitted on July 26 after his condition worsened.
He died at 8.40am on July 27 just 25 minutes after a scan revealed that he had endocarditis which had attacked a heart valve.
A doctor had requested a scan the day before but was told the machine was not available.
Staff nurse Lisa Arnold said: “I was told the machine was not working.”
Consultant Dr Andrew Leonard, who saw Mr Hemsley on July 2, apologised to the family and said: “The impression was that his condition was not life threatening. We failed to realise he was gravely ill.”
But top heart expert Dr Rachel James told the inquest that Dr Leonard could not have known from the symptoms that the disease had taken a hold.
She said: “The disease can present itself in unusual ways and there is no evidence that would lead to it being diagnosed on July 2.”
Coroner Alan Craze said: “When he was readmitted on July 25 it should have been blindingly obvious that something serious was going on.
“Nobody seems to be able to answer why no-one in the hospital was able to get hold of a cardiogram for a whole day.”
The alarm was raised by Newington Ward staff-nurse Katrina Coffee who told the inquest: “This man was deteriorating and needed cardiac monitoring.”
A junior doctor then recommended he be transferred.
But a bid to get him transferred to the cardiac care unit was opposed by Sister Myleen Spry, who was concerned that he may still have a stomach infection despite three tests showing negative.
Mr Craze said: “With hindsight Sister Spry got it wrong. There is no doubt whatsoever he should have been in the cardio unit. For a junior doctor to raise concerns about a patient and say he should be admitted to the unit and that to be refused by a sister is not optimal.
“As is so often the case there was a lack of communication here. No-one was prepared to take this up a level.”
He added: “It is very worrying. We have already established it would not have affected the outcome but the quicker you can get these diagnostic tests done the better.
“If it had been a situation where the outcome could have been different this would be a very serious case indeed.”
Nursing Head Lisa Scragg, who carried out a ‘serious incident’ investigation for the hospital, said: “There are now two heart scanners at the Conquest.
“We have been looking at practices with the trust and looking at areas where there may be problems. We have really learned from this in the past 18 months.”
The coroner, recorded a verdict of death by natural causes and said: “The die was cast by the second time he went in and I cannot see any situation or circumstances where his life could have been saved.”