Women with an irregular heart beat are more likely to suffer heart disease and die than men with the same condition, research suggests.
Experts said the findings show that women should receive potentially different doses of treatment or should be treated more aggressively than men.
A team, including experts from Oxford University, analysed 30 studies of more than four million people from between 1996 and 2015.
Women with atrial fibrillation (AF) in the group were more likely to die from any cause than men with AF (12% higher chance) and had almost double the risk of stroke, almost double the risk of death from heart disease and a 16% higher chance of heart failure.
The authors said it was unclear what caused the differences between women and men.
AF occurs when the heart's upper chambers contract randomly and sometimes so fast that the heart muscle is unable to relax properly between contractions.
This leads to an irregular and often abnormally fast heart rate, and affects up to one in 10 people aged 65 and over.
A normal heart rate should be regular and between 60 and 100 beats a minute when a person is resting.
In some cases, people with AF have hearts that beat much faster than 100 beats a minute.
This can cause problems including dizziness, shortness of breath and tiredness, although some people have no symptoms.
Treatment can include medication to prevent a stroke or control the heart rate and rhythm, and cardioversion - where the heart is given a controlled electric shock to restore normal rhythm.
June Davison, senior cardiac nurse at the British Heart Foundation, said: "Currently AF is often undiagnosed and under-treated in both women and men. This study suggests greater attention should be given to the identification of AF in women.
"It's important that healthcare services for the prevention and treatment of AF take into account the different effects of gender on the condition.
"More research is needed to find out more about the underlying causes of these differences and the BHF is currently funding millions of pounds of research into better understanding and treating AF."