Heart attacks have become more common in middle-aged women over the past two decades but a woman's chances of survival have also greatly increased, two new American studies have shown

While the incidence of heart attacks has increased, all women - and especially those younger than 55 - have also experienced a greater increase than men in their chances of survival following a heart attack.

In the first study, Amytis Towfighi, M.D., of the University of Southern California, Los Angeles, and colleagues analyzed data from U.S. adults age 35 to 54 who participated in the National Health and Nutrition Examination Surveys (nationally representative surveys conducted by the government) during 1988 to 1994 (4,326 participants) and 1999 to 2004 (4,075 participants).

The researchers assessed how often men and women had heart attacks and also compared their Framingham coronary risk score, a measurement of heart disease risk over 10 years that includes factors such as age, cholesterol levels, blood pressure and smoking history.

In both study periods, men age 35 to 54 years had more heart attacks than women in the same age group. However, the gap narrowed in more recent years as heart attacks decreased in prevalence among men and increased in prevalence among women (2.5 percent of men and 0.7 percent of women reported a history of heart attack in 1988-1994, whereas 2.2 percent of men and 1 percent of women did so in 1999-2004).