Experts say keeping bad habits like drinking, smoking and overeating could put younger women at an increased risk of heart disease.
Researchers at Oxford and Liverpool universities have found that deaths from coronary heart disease are dropping in all groups except in women aged below 50.
They found that death rates from heart disease increased steadily in all groups throughout the 20th century and peaked in the 1970s.
Since then, researchers found that there had been a steady decline in the mortality rates as the dangers of smoking became apparent and people quit, while diagnosis of heart disease became faster and access to effective treatments improved.
However, mortality rates in women aged below 50 had levelled off and even risen.
Experts said that the reason was the increasing levels of obesity and lack of exercise, but particularly because the number of women smoking and drinking heavily was increasing.
Women often do not consider themselves to be at risk of heart disease and so go to their doctor with symptoms much later and are diagnosed at a later stage in the condition, when it is more difficult to control.
Dr Ian Campbell, a GP and the medical director of the charity Weight Concern, said one fifth of heart disease cases could be avoided if people maintained a healthy weight.
"These findings are disturbing but not surprising," he said.
"Middle-aged women have multiple risk factors for heart disease - they are likely to have been inactive for 20 years or more, obesity has trebled in this age group in the last 25 years and they are continuing to smoke.
"Fundamentally, this is about an unhealthy lifestyle," he added.