AN EXTRAORDINARY row flared yesterday in medical circles after a doctor at the centre of the controversial ox valve heart technique claimed his staff were the target of a ''dirty tricks'' campaign. The Chinese University of Hongkong, which has pioneered the use of the innovative operation, said its technique had been attacked recently partly out of professional jealousy. In a strongly-worded statement, the university defended the treatment of rheumatic heart disease with the valve made from the cover of ox hearts, claiming there was no valve failure ''other than one possible death which may be attributable to known technical problems''. The chairman of the university's Department of Surgery, Professor Arthur Li Kwok-cheung, said in the statement it was ''demeaning to the whole profession'' to ''make mischief'' out of a scientific study. Professor Li refused to disclose the exact number of patients who had died - a matter of concern among cardiac experts who remain sceptical about the success of the technique. The university said it could not disclose the figure before an investigation by a visiting academic was completed. It had earlier stated that ''more than half of the patients still survived''. Outspoken Professor Li, who is also Dean of the medical faculty, also claimed it was ''but one in a concerted campaign to discredit the Prince of Wales Hospital'' - the teaching arm of the university. The statement suggested the campaign was orchestrated in an attempt to ''gain advantages in resource allocation''. The university's statement said: ''. . . we now have a situation whereby not only the Prince of Wales Hospital is being defamed, but more regrettably, those patients that we have operated upon are frightened that all may not be well, adding further anxieties and stress to their already serious illness''. Grantham Hospital's Professor Mok Che-keung, who is one of the many cardiac experts questioning the heart valves, said he did not see any links between resource allocation and the debate over ox valves.