When my Aunt Gert suffered a heart attack in her mid-70s, the examining doctor told her that it was not her first. Tests done to assess the damage to her heart revealed a section of dead muscle from a previous unrecognized heart attack. Sometime in the past, she had had what doctors call a “silent myocardial infarction,” or S.M.I., silent in that any symptoms she might have had at the time did not register as related to her heart and were not brought to medical attention.

My aunt was lucky. She survived her second heart attack and, by keeping cardiac risk factors under control, lived another two decades without further heart-related problems.

There are millions of people walking around in this country who, like my aunt, are oblivious to the fact that they have had an S.M.I. and face an increased risk of having another, more obvious one that could cause severe heart damage and possibly death.

You might think a silent heart attack is better than a recognized one: “What you don’t know can’t hurt you.” Unfortunately, it can. Although knowing you’re at risk of a heart attack can be emotionally distressing, not knowing can have much more serious consequences, prompting you to continue living in ways that endanger the health of your heart and your life.