People are being urged to talk to the women in their life about the risks of heart disease.
The British Heart Foundation (BHF) said too few women are aware that it is the biggest killer of women and more needs to be done to raise awareness that it is not just a man's disease.
Heart and circulatory disease kills more than 80,000 women in the UK each year and 17.3 million women worldwide.
In the UK, 3.5 million women are living with some form of heart or circulatory problem.
The warning has been issued to mark International Women's Day today.
Maureen Talbot, senior cardiac nurse at the BHF, said: "Too few women realise that heart and circulatory disease is their biggest killer. I hope people will use International Women's Day as their prompt to have a straightforward conversation with the woman they love about her heart health.
"Ignorance is fuelling women's heart risk. So while our ask is simple, the impact really could save lives.
"On a day when women are thinking and talking about how to improve their lives, we also want them to include one, potentially life-saving, conversation with another woman they love about how they look after their heart.
"Sadly most women are oblivious to the fact that heart problems are the biggest killer of women in the UK. If more women knew they were at risk, they could do something about it, whether that's losing a bit of weight, quitting smoking or just taking the dog out for longer walks."