The deaths of up to 250 patients who died following heart surgery at an NHS hospital are to be reviewed.All the patients underwent surgery at St George’s Hospital in Tooting, south London, between April 2013 and September 2018.The review, commissioned by NHS Improvement, comes after the hospital suspended complex heart surgery last year to improve services.A leaked report previously suggested that poor relationships at the cardiac unit contributed to a higher mortality rate.The trust said families of cardiac surgery patients who died during the review period will be contacted if the panel identifies “any significant concerns about their care”.Jacqueline Totterdell, chief executive at St George’s, said: “It is absolutely essential that patients and their families have full confidence in the care our cardiac surgery team provide – and this review of past deaths will be a key part of that process.”The review only applies to cardiac surgery at St George’s, and does not include other associated specialities – for example, cardiology.The panel will examine the safety and quality of care that patients who died during or after cardiac surgery at St George’s received during the review period.They will do this by reviewing the medical records of deceased cardiac surgery patients, as well as any investigations conducted by the Trust at the time of the patients’ deaths. The panel is likely to review between 200-250 deaths as part of this process, which will take place between six and 12 months to complete.The period between April 2013 and March 2017 has been identified as a time when the trust had a statistically higher mortality rate compared with the other 31 cardiac surgery centres in the UK.The panel will also review deaths between April 2017 and 1 September 2018, when improvements were being made.Last summer a leaked report warned that a “toxic” feud between two rival camps at the unit left staff feeling a high death rate was inevitable.St George’s Hospital heart unit was consumed by a “dark force” and patients were put at risk, the investigation concluded. The damning review was written by former NHS England deputy medical director Mike Bewick in response to higher mortality rates at the hospital.He found the south London facility had a cardiac surgery death rate of 3.7 per cent – above the national 2 per cent average, reports said.Internal scrutiny was said to be “inadequate” and the department was riven between “two camps” exhibiting “tribal-like activity”.Professor Bewick’s review was quoted as saying: “Some felt that there was a persistent toxic atmosphere and stated that there was a ‘dark force’ in the unit.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Conversations with 39 members of staff revealed they were shocked by the death rate, but “most felt that poor performance was inevitable due to the pervading atmosphere”.The independent reviewer examined “disturbing and often difficult information”, concluding an “existential threat” was posed to the unit because staff and patients would go elsewhere if problems persisted.