Continuing problems were linked to smoking and depression
One in five people recovering from a heart attack is still having chest pain a year afterwards, a US study suggests.
The journal Archives of Internal Medicine reported some suffered angina every day, despite bypass surgery.
A Colorado University-led team, which quizzed nearly 2,000 patients, said it was linked to smoking or depression in some cases.
A spokesman for the British Heart Foundation the study could help doctors spot who was at highest risk.
Chest pain, or angina, is a common symptom of heart disease, and doctors expect some heart attack patients to continue to have it, regardless of efforts to treat their underlying disease.
This study, carried out by researchers at the Denver's Colorado University, and the city's Veteran's Affairs Medical Center, tries to shed light on how extensive the problem is.
The team looked at the progress of 1,957 patients, who filled in questionnaires a year after their heart attack.
In all, 19.9% of the patients said they still had angina pain one year after their attack, and although this was once a week or less for most, 1.2% of them had daily pain.
Smoking and depression
The questionnaires revealed that those most likely to have chest pain were younger men who had undergone heart bypass operations, or men who smoked or had depressive symptoms.
The researchers said these links might help doctors monitor "at risk" patients.
A spokesman for the British Heart Foundation said: "This study helps us to understand what factors may cause people to experience chest pains one year after heart attack.
"Identification of these factors - for example smoking or depression - can help health professionals recognise people who may be at risk of developing this problem.
"Targeted services for these people - such as helping them quit smoking - may help to improve the quality of life and health of heart patients by alleviating or preventing angina".