In the 1700s, the heart was linked to emotion—a vestige from the days of Aristotle, who believed that the heart was the seat of all feelings, particularly anger. The Scottish surgeon John Hunter was one of those who linked heart disease to emotional excesses. His own fatal heart attack was caused, according to his doctors, by his angry temperament.

In the late 19th century, the influential Canadian physician William Osler challenged this idea, arguing that heart disease was caused by stress, not anger. The typical heart patient, he believed, was a “keen and ambitious man, the indicator of whose engine is always ‘full speed ahead’”—a “well ‘set’ man from 45-55 years of age, with a military bearing, iron-gray hair, and a florid complexion.” For Osler, heart disease was almost a badge of honor, the mark of a hardworking capitalist man.

For the next 100 years or so after Osler’s writing, that was the image that stuck. Throughout the 19th and early 20th centuries, doctors believed that the people most prone to heart attacks were of the type that Osler described: ambitious, successful, and most importantly, male.

It wasn’t until the 1950s that heart disease was linked to diet, exercise, and other physical factors rather than emotional causes—but even then, it remained a man’s condition. The American scientist Ancel Keys, who authored several landmark studies on diet and heart disease in the 1960s and ‘70s, used middle-aged men in most of his research, a pattern that repeated itself in many of the most important cardiology studies of the next few decades. For example, the 1982 Multiple Risk Factor Intervention Trial, one of the first to establish a link between cholesterol and heart disease, involved 12,866 men and no women; the 1995 Physicians’ Health Study, which found aspirin to reduce the risk of heart attack, involved 22,071 men and, again, no women.

The focus on men extended to medical education as well. “When we were taught about it at medical school [in the 1970s and ‘80s], no one explicitly said, ‘This is a man’s disease,’” said the New England Journal of Medicine editor Harlan Krumholz, who started studying heart disease in young women in the early ‘90s as a medical researcher. “The case studies at that time, 20 or 30 years ago, were focusing on the man as the prototype of the problem.” Krumholz recalled the iconic drawings of Frank Netter, arguably the most famous medical illustrator of the 20th century—Netter’s illustrations, which medical students still use to learn about human anatomy and a variety of diseases, only rarely depicted women with heart disease.

The absence of female subjects in medical textbooks and in research papers means many doctors simply didn’t know how to treat heart disease in women, or even how to recognize it. Symptoms can differ by gender: Men are likely to get chest pains when they’re having a heart attack, for example, but women may instead feel discomfort in the neck, jaw, shoulder, back, or arm. Many women also experience nausea, vomiting, or a feeling similar to indigestion, as Larko did.