An investigation has been launched into the heart transplant programme at Papworth Hospital in Cambridge after it reported a sharp increase in the number of patient deaths.

Heart transplant operations at the hospital were suspended this week after it emerged that seven of the 20 (35 per cent) adult patients who have had the operation since January died within 30 days of the procedure, well above the hospital's usual mortality rate of 7 per cent.

Papworth Hospital informed the Department of Health of the unusually high mortality rates and investigators from the Healthcare Commission were ordered to conduct a preliminary review of the hospital's heart transplant programme.

A spokesperson for the Healthcare Commission said: "A team, including clinical and technical experts, began the review on Monday [29 October]. This is an ongoing investigation that will take two weeks to complete. We're not going to go into details but you can safely assume officials from the Healthcare Commission are inside Papworth conducting their investigations."

The investigators will review individual case notes of the patients who have died since January to check the quality of care they received and to see if there are any common factors. They will also investigate whether the hospital did enough after discovering the increase in deaths to try to find out its cause.

Papworth Hospital refused yesterday to confirm how many people waiting for transplants had been affected by the suspension but said the number would be small.

"We would normally perform one or two heart transplants in a two-week period, so only a small number of patients are affected," said a spokesperson for the hospital. "Should an opportunity arise for one of these cases to be transplanted, clinicians in Papworth will discuss and agree with the external advisers involved in the review how to manage the patients."

The unusually high death rate at Papworth mirrors a similar spike in post-operation fatalities at St George's Hospital in Tooting, south London, which was also forced to stop all heart and lung transplants in 2000 after post-operation fatalities jumped to five times the national average.

A subsequent investigation found that many patients had been picked for transplant operations even though their physical condition should have ruled them out and also discovered highly unsanitary conditions inside the hospital.

Papworth is one of five centres in the UK allowed to practise heart transplant operations, the others being the Freeman Hospital in Newcastle; Harefield Hospital in Middlesex; Manchester Royal Infirmary; and the Western Infirmary in Glasgow.

Papworth has a reputation as one of the country's top heart and lung transplant centres with a previously excellent record on post-operative survival. Surgeons at the hospital have been at the centre of some of the most significant transplant breakthroughs including the first successful UK heart transplant in 1979 and the first beating heart transplant, which was performed last year.

Seventy-four people are currently listed as waiting for a heart transplant and 155 people underwent the operation last year.

Organ donor campaign groups were keen yesterday to emphasise the benefits of transplant operations and said, that for most people, a heart transplant meant a new lease of life.

"A heart transplant remains one of the most effective treatments for those suffering with heart failure and in the past five years 750 lives have been transformed by this life-saving treatment," said Noel Davies from the UK Transplant group. "The long-term survival rate of patients with a transplanted heart is high with 80 per cent of recipients still alive one year on, while 69 per cent survive to five years after a transplant."

Although heart transplant operations have been suspended at Papworth, the hospital said all other services, including lung transplantation, were unaffected and will continue as normal.

A centre of excellence in cardiac care

Ever since surgeons at Papworth in Cambridgeshire carried out the UK's first successful heart transplant operation in 1979, the hospital has been regarded as one of the world's leading heart centres.

In July it staged the first interactive public broadcast of a British hospital operation, during which the audience were able to ask the surgeon questions as he performed open-heart surgery. Last year surgeons performed the UK's first "beating heart" transplant, where the organ was kept supplied with blood until it was inserted into the patient.

Heart transplant operations are notoriously complicated procedures that involve large surgical teams. At Papworth a team of 10 people is usually involved in the operation – two surgeons, three or four nurses, an anaesthetist and their assistant, and a transplant co-ordinator. The operation usually takes between four and six hours. Ideally the organ needs to be ready for surgery no longer than four hours after it has been removed from the donor.

Despite the recently discovered high post-operation mortality rates, the hospital usually has one of the best track records for heart transplant patients surviving the precarious 30 days following the operation. Last month, Papworth achieved the top score of "excellent" in the Healthcare Commission's 2006-07 annual NHS performance ratings. The hospital is asking patients or relatives with concerns to call 01480 830541.