Writing in the report, published in the JAMA Internal Medicine, the researchers said that depending on a woman's overall susceptibility to heart disease and how the radiation has been delivered, the risk could be anywhere between 0.05 percent to 3.5 percent.
Women who already have an increased risk of heart disease and who receive radiation therapy on their left breast when lying on their back have the greatest risk of heart disease.
"Our findings confirm that the radiation exposure associated with left-breast cancer radiotherapy is associated with a generally small, increased risk of heart disease later in life. Of course, that side effect needs to be balanced against the fact that lumpectomy plus radiation is of well-proven efficacy for treating early stage breast cancer. All cancer therapies involve balancing benefits and risks", lead researcher David Brenner said.