THE most painful part of a coronary artery operation was having to give up fatty foods, cigars and the fast life, according to one Hongkong executive who has had the operation. Another executive said the Governor, Mr Chris Patten, would have been conscious yesterday and viewing the operation which proved the ''wonders of medical science''. STAR TV executive vice-president, Mr Arnie Tucker, sympathised with Mr Patten, but said a similar operation he had on his heart late last year was relatively painless. ''The worst thing was having to change my diet afterwards. You can't eat all the wonderful foods in life like hamburgers, steaks and icecreams,'' he said. ''I've had 50 years of wonderful living at every fast-food outlet in the world and pastrami sandwiches for breakfast. I like my food, but when you get a clogged artery and you're told you've had a minor heart attack it's an incentive to change your lifestyle.'' Mr Tucker had the operation at the Adventist Hospital on December 18, but even then was reluctant to sacrifice work to ease stress. He even took a portable telephone into intensive care. Neither has he managed to do as much exercise as desirable. ''I will have to do something, not too high impact, maybe lots of walking to get my heart pumping.'' He advised Mr Patten to ''take the experience to heart and listen to the doctor, but live a life too''. ''The operation is a piece of cake and you can't go and live in a monastery eating seaweed. I'll probably still even smoke a cigar now and then, but I'll probably go for yoghurt instead of ice cream,'' Mr Tucker said. Trade Development Council publicity manager, Mr Howard Coats, had a similar operation at the Adventist in December. ''It's an amazing operation. They just give you a local anaesthetic and you lie back and watch yourself on a scanner. You watch the catheter going through an artery and the heart is outlined on the screen like a massive ginseng root gyrating.'' He said the surgeon explained step by step what was happening and the patient could witness the physical change in the artery as the catheter balloon widened the narrowed sections. ''In three or four days there is only a bit of pain at the point of entry.'' Mr Coats has since had another operation on the artery in his arm. ''It's just like night-viewing on the television. It's brilliant technology. ''When we were growing up people would talk about heart victims taking a year or two to recover but not now. It might be typical of Hongkong, but it's like a garage - they wheel you in, tinker a bit, give you a recoat and push you out and back to work.'' Personal fitness trainers would have Mr Patten doing push-ups on the back of his office chair, joining an aerobics class, or walking up and down the steps of Government House with a rubber band around his legs. Two top trainers qualified in physical education have suggested Mr Patten either switch off from stress and on to fitness, or adopt a fitness routine for someone on the run. Personal trainer and world-standard aerobics competitor, Mr Sport Stewart, has suggested Mr Patten incorporate it into his working day and his wardrobe. ''He could easily do some push-ups hanging on to his chair, or put some weights in his briefcase, or strap some weights to his legs - no-one would even see them under his dress pants.'' But Mr Stewart stressed that personal details ranging from Mr Patten's sleeping positions to culinary weaknesses would have to be scrutinised, then incorporated into a personal programme. The next step could be the most important - mental preparation. ''He sounds like someone who needs first to work on relieving his mental stress so I would teach him how to switch off psychologically. Then I'd probably ease him into the programme using light weights,'' Mr Stewart said. He also suggested Mr Patten conduct some of his meetings as tennis matches or swimming sessions. This is a common practice in the United States to provide a mental break, exercise, and an alternative to stressful boardroom battles or fattening dinner deals. The assault on Mr Patten's diet could ultimately be more severe than the disruption to his work schedule, but it would also be gradual. ''I might start by suggesting he cut milk or cream out of his diet, but I would have to look carefully at all the cholesterol in his diet. ''If he is having a couple of eggs for breakfast that already reaches the suggested cholesterol maximum for the day. If he is going on to lunch or dinner in restaurants and having dessert and coffee then he would be easily over the limit.'' Another personal fitness trainer, Miss Liz Bradley, who has degrees in nutrition and physical education, said Mr Patten might have to get up half an hour earlier in the morning to allow for exercise, probably a minimum of 20 minutes exercise three times a week. A walk or jog up Bowen Road or the Peak, however, could be highly stressful if reporters and security men are pounding the pavement behind him, so he may be better off exercising at home. She was not convinced about the tennis. ''Some activities also increase stress. For example, tennis is no good for him because it is competitive.''