Our hearts kill more of us than all kinds of cancer combined.

Surprise No. 2: I learn that Hal’s attack and mine are textbook illustrations of how vivid the gender differences can be. I learn that men more typically have “crushing” pain; women, nausea. That women are likelier to have early warning signs, such as unaccustomed fatigue or insomnia (unaccustomed: That’s the key word here). That we are likelier — this spooked me and kept me, for months, glued to calendars — to die within a year of a heart attack. That our symptoms can be so varied and nuanced that we feel no fear, seek no help, and possibly die — which may be why, although more men have heart attacks, a greater percentage of women die of them.

All these gender distinctions strike me as marvelously curious. I begin, as I did during Hal’s many emergency admissions, interviewing doctors and nurses and keeping a journal.

A nurse practitioner offers a graphic tutorial. Big, broad, a Valkyrie, she plants herself at the foot of my bed, puts one hand beneath her nose, as though in salute, and the other at her pelvis, and says, “In women, from here to here, anything could be a symptom.” Thus encompassing jaw, neck, throat, back, shoulders, chest, arms, diaphragm, abdomen.

“That’s terrifying,” I say.

“It’s just information,” she says. “It’s good to be informed, not terrified.”

The question looms: Why should such differences be?

Answer: Nobody knows for sure.

There are theories. Many. It may be because a woman’s arteries are narrower than a man’s, or because her microvascular system functions less efficiently, or because her heart beats faster (verging, this, on metaphor), or because it takes longer to relax between beats, or...

But if it is not well understood, we do have one good — bad — reason it is not well understood. The reason is gender bias.

Until shockingly recently — in fact, until this millennium — there was minimal research on women’s heart attacks because of widespread belief in the medical community that women did not have heart attacks. (When the American Heart Association introduced its Prudent Diet in the 1950s, it issued a pamphlet titled “The Way to a Man’s Heart.”