Heart disease kills more women in the U.S. than any other disease. But when you are a vibrant 21-year-old, it’s the last thing on your mind.

Megan Johns suffered a heart attack one day before her college graduation ceremony.

“I had pressure in my chest, and it felt like a stack of books was on my chest – and then my left arm was tingling and it felt heavy,” Johns said.

Johns, a vegan, didn’t eat any meat or dairy, and she worked out regularly – so the heart attack did not make sense.

Initially, her doctors blamed her birth control – but after dozens of tests and not many answers, Johns went to the Cleveland Clinic where doctors ordered a unique blood test.

The result? A genetic link to heart disease called lipoprotein a.

"It is a special type of cholesterol that actually increases the tendency to have heart attack and stroke by making the cholesterol sort of thick and more clot forming," said Dr. Leslie Cho, director of the Cleveland Clinic’s Women’s Cardiovascular Center.

Johns’ family was tested for lipoprotein a, and it turned out her mom was carrying the same biomarker.

Now that she knows about it, she can help control it.

“I have a predisposition to high cholesterol, and even though I eat healthy, it always will be elevated unless I take medication to do something about it,” said Johns’ mother, Kim.

"It's an easy thing to know what your risk is, and then when something, if something ever happens, you can listen to your body and know what it's telling you."

Johns takes medicine to control her high cholesterol, and she continues to pay attention to her diet and exercise.

One year after the heart attack, the University of Dayton invited her back to officially accept her diploma.

"I was relieved to find out something, to just be able to know and feel confident that I know what's wrong and that I can now take care of myself," Johns said.