Fewer than half of smokers give up after a life-threatening heart problem, researchers have found.
Smokers find it hard to quit - even after a heart attack
A European survey of 5,500 patients in 15 countries looked at people who had experienced heart attacks, blocked or narrowed arteries and angina.
Researchers writing in the European Heart Journal said the findings were "unbelievable".
They called for more intensive smoking cessation programmes to get the health message across more effectively.
The survey was carried out in 1999 and 2000.
Patients were interviewed about 16 months after their hospital treatment.
They were asked if they had ever smoked, whether they had smoked in the month before hospital admission and whether they currently smoked.
People were also breath-tested for carbon monoxide to detect smokers who denied their habit.
Overall, 2,244 (40%) of the patients were smokers before their illness.
Virtually all had been advised to stop smoking, but just 48% had done so.
Younger patients were less likely to quit.
Those with angina were less likely to stop than heart attack patients, which researchers said could be because of a lack of awareness of their risk.
However, both groups have the same mortality risk, they said.
Dr Wilma Scholte op Reimer, of the Erasmus University Medical Centre in Rotterdam, the Netherlands, who led the study, said it was "unbelievable" so many carried on smoking after a life-threatening event for which the habit is a major risk factor.
"It makes me wonder if they are truly aware of the risk that they are taking," she said.
Dr Scholte op Reimer said there may be a difference between patients having the general knowledge that smoking is a bad habit, and understanding the risk they themselves faced.
She said it was important smokers had access to support from stopping-smoking programmes, and access to nicotine replacement therapies, if necessary.
The research was a follow-up to a similar study five years earlier, which found similar results.
Another survey is planned to see whether the situation improves.
June Davison, spokesperson for the British Heart Foundation, said: "It is saddening to hear that even after a heart attack, one of life's biggest health warnings, a large proportion of smokers don't manage to give up.
"Stopping smoking is one of the most important decisions you can ever make to improve your health - even more so if you have coronary heart disease.
"Quitting after a heart attack significantly reduces the risk of death. For those without heart disease, by stopping smoking now, their risk of a heart attack will have dropped by about half by next autumn."
She added: "Although we're not bottom of the European league table for heart patients quitting, the sad fact remains that in the UK every half an hour another smoker dies of heart disease.
"Studies like this one reinforce the importance of support services for people trying to quit."