HONGKONG'S medical profession includes many top cardiologists trained in the most up-to-date techniques but the centre where Mr Patten will be treated at Queen Mary Hospital is almost 40 years old. The recent successful heart transplant carried out at Grantham Hospital proved that the territory could perform advanced operations, the vice-chairman of the 4,000-strong Hongkong Medical Association, Dr Lee Kin-hung, said yesterday. ''Hongkong's heart diseases treatment is comparable with the best countries in the world,'' Dr Lee said. He estimated that there were more than 100 cardiologists in the territory. The major hospital for heart patients is Grantham on Hongkong Island, which provides strong cardiac surgical back-up and 24-hour emergency services. The Lewis Cardiac Catheterisation Laboratory where Mr Patten will be operated on today was set up in the Professorial Block at Queen Mary, the teaching hospital of the University of Hongkong, in 1956. It was designed especially for heart disease treatment and diagnosis. The laboratory was recently renovated. According to the latest official figures, 4,858 people were killed by heart diseases in 1991 - 16.9 per cent of the total number of deaths. The teaching hospital of the Chinese University, the Prince of Wales, last year was the first in the world to successfully use an innovative artificial heart valve made from the outer covering of ox hearts. About 10 patients have been treated so far.