For decades, Billie Jean King has broken barriers, fighting for gender equality on the tennis court and  becoming a hero to the LGBT community. The 39-time Grand Slam title winner— she has a  record 20 championships at Wimbledon— now has a new fight. King teamed up with Janssen Pharmaceuticals, Inc. to raise awareness about the risk of stroke for those who have atrial fibrillation (AFib).

AFib, the most common type of arrhythmia, is an irregular heartbeat where the top two chambers of the heart beat at a different rhythm than the bottom two. The condition can cause blood to pool in the upper chambers of the heart, instead of pumping completely into the lower chambers, resulting in blood clots. A clot can break free and travel to the brain, where it can block blood flow, leading to a stroke.

King’s first sign of trouble came after playing a game of tennis with a friend.

“Got out of the taxi, and I got really dizzy and I thought I was going to black out and I never get dizzy. I’ve never fainted,” King told FoxNews.com, adding, “My heart was beating, I thought it was going to come out of my chest and I could tell it wasn’t regular.”

Many people would be surprised to learn that a celebrated athlete who has led a healthy lifestyle would develop a heart condition, but King says that it is common among athletes. Dr. Manny Alvarez, the senior managing editor of health news at Fox News, agreed, adding that athletes tend to put extra pressure on their hearts over time. Other factors such as diabetes— which King has— age, high blood pressure and a family history may play a role.

King visited a cardiologist and was prescribed daily blood thinners and underwent a catheter ablation. According to the Mayo Clinic, the procedure involves threading catheters through blood vessels to the inner heart, where electrodes at the catheter tips use radiofrequency energy, extreme cold or heat to destroy triggers that cause the erratic heartbeats.

The treatments were successful for King, who said she feels fantastic and has not allowed the diagnosis to change her lifestyle as she continues to eat well and exercise.

Now, King is raising awareness of the increased stroke risk for AFib patients by promoting MyAFibRisk.com. On the website, patients answer questions to help discuss stroke risk management with their physicians. AFib raises the risk of stroke by five times and accounts for 15 to 20 percent of all stroke incidents.

For every person with the condition who visits the website and calculates their risk, Janssen Pharmaceuticals, Inc. will make a contribution to Mended Hearts, a non-profit peer-to-peer support network that offers help to heart disease patients, their families and caregivers.

Click to visit MyAFibRisk.com.