An analysis of data for more than 58,000 women in the U.K. Biobank found that both short (less than 21 days) or long (more than 35 days) menstrual cycles were associated with the development of cardiovascular disease, heart attack or atrial fibrillation (AFib). Short or long menstrual cycle length was associated with a 19% higher risk of heart disease among those women compared to women with menstrual cycle length between 22 to 34 days. Irregular menstrual cycle length was associated with a 40% higher risk of atrial fibrillation.