International heart experts warned yesterday that the thousands of Australians popping anti-oxidant pills to ward off coronary disease could be increasing their risk of cancer. An American heart disease expert, Dr David Harrison, said preliminary studies into the use of anti-oxidants - vitamins E, A and C - had indicated that in 'some cases it might actually make coronary disease worse''. Speaking at the Cardiac Society of Australia and New Zealand annual conference, Dr Harrison said the mass-marketing of anti-oxidants appeared to have been premature.