The classical music world was stunned when, earlier this week, a new biography of Benjamin Britten claimed that the composer's death was hastened by syphilis.

But now the cardiologist who cared for Britten during the last three years of his life has cast doubt on the revelations, telling the Guardian that he believes it is "extremely unlikely" that Britten had the venereal disease, and "complete rubbish" that his surgeon would or even could have covered up the condition, as Paul Kildea's biography, Benjamin Britten: A Life in the 20th Century, suggests.

Britten's medical notes, seen by the Guardian but not available to Kildea before he wrote his biography, make no reference to syphilis, even by way of any accepted euphemisms for the infection current in the 1970s.

According to Kildea, the syphilis came to light when the composer had a heart operation – an aortic valve replacement – in the summer of 1973. The biography states that when Britten's surgeon, Donald Ross, opened him up he found "the aorta was riddled with tertiary syphilis".

However, Michael Petch, now a consultant cardiologist who was the senior registrar who cared for Britten at the National Heart hospital that summer, and who has re-read the operation report and other materials, told the Guardian that Kildea's account was "unbalanced". Though syphilis was "not impossible", he said, "it does not fit with everything else … there is no serological, bacteriological, pathological or histological support for the diagnosis. My belief is that the original story about Britten's death [that he simply died from heart failure, unaffected by syphilis] should be allowed to stand."

The source for Kildea's account is Hywel Davies, another cardiologist, in whom, according to Kildea, Ross confided his secret diagnosis some years after the operation, having initially covered up the truth because of the stigma attached to the venereal disease. (Ross is now in ill-health, and could not be quoted either for this article or for Kildea's biography.)

Kildea told the Guardian: "I'm thrilled medical papers have turned up, but they don't change the import of my final chapter, which Petch can't rule out, and which Davies repeats: Donald Ross told him Britten's aorta was syphilitic, no matter what he said or wrote."

But according to Petch, the notion that Ross could have covered up his suspicions of syphilis in the operating theatre was "rubbish": "It takes 14 people to do a heart operation. It would have been impossible to have kept it secret."

Petch went on to treat Britten, visiting his home in Suffolk twice a year, up until his death in 1976.

"If Ross had thought there was syphilis, he would have called in a venereologist. He might have been discreet – he might have asked the specialist not to visit the National Heart hospital for example. But Ross would have let me know, and so would have [Petch's boss, consultant cardiologist] Graham Hayward."

Beng Goh, a consultant physician and expert in syphilis, has examined the medical records and has separately concluded that Britten was "unlikely" to have been suffering from cardiovascular syphilis (a form of tertiary syphilis that affects the aorta and aortic valve) as claimed.

According to Goh, the tissue samples taken from the composer's aortic valve, and written up in the medical notes, crucially revealed no evidence of syphilis. "To diagnose syphilitic aortic valvular disease, there should be evidence of vasculitis – inflammation of blood vessels," said Goh. No such inflammation was reported.

In addition, said Goh, the notes reveal "there no other clinical features ... that would suggest syphilis as a possibility". For example, said Goh, in such a case one would expect to see calcium deposits on the aorta – "but this was not present in the chest x-ray".

Goh also cast doubt on the notion aired in the biography that in 1940 a bout of streptococcal tonsilitis that left him sweating and hallucinating was "his body in fact reacting to syphilis, now in its secondary stage". According to Goh: "Sweating and hallucination are most unlikely to be symptoms of secondary syphilis."

Composer Colin Matthews, who was Britten's assistant in the 1970s and is a trustee of the Britten-Pears foundation, said: "Whatever the outcome of these investigations – and it's hard to see how anything can be proved either way – it makes no difference to Britten's standing as a composer."

Kildea's book theorises that Britten caught syphilis from his longstanding partner, Peter Pears, whom he speculates may have been a symptomless sufferer from the disease.