Image taken from Gray's Anatomy

Every day, millions of schoolchildren across the US put their right hands over their hearts and recite the Pledge of Allegiance. Curiously, about 1 in 10,000 should be using the other hand.

A small percentage of people—in the US, about 0.01%, or 1 in 10,000—has a congenital condition known as “situs inversus,” in which his or her internal organs are a mirror image of the typical organ layout: thus, the liver and gallbladder lie on the left, and the stomach, spleen, and heart on the right. (People with this condition are commonly called “dextrocardiacs,” though this term refers specifically to the heart and is therefore incomplete.) Because situs inversus presents few symptoms, many people do not discover their organs are inverted until later in life, often after a medical procedure.

Despite its orientation, the heart itself is generally unaffected. People with situs inversus are only slightly more at risk for heart disease—a 3-5% incidence, as opposed to the average 1%. And the only other symptom is a predisposition to sinus infections and chest colds, which manifests itself in just 20% of people with SI. This symptom, known as Kartagener syndrome, occurs when the body’s cilia (the tiny, moving hairs that flush foreign objects out of the respiratory tract) are immobile from birth. Because half of people with Kartagener syndrome randomly have situs inversus too, a sort of ongoing chicken-and-egg debate has arisen over which causes which. There are also several cases of mirrored twins, in which one is situs solitus (or normally arranged) and the other situs inversus.

Organ reversion does not typically affect a person’s lifespan, but—prior to being diagnosed—he or she is at risk for some disquieting mix-ups. For example, a seemingly benign pain in the lower left of the abdomen can end up being appendicitis; a tingling right arm, a heart attack. Often, people who know they have SI wear bracelets to indicate their dextrocardia, so that in a medical emergency doctors know where their heart lies. Notable dextrocardiacs include actress and comedian Catherine O’Hara; Washington Wizards draftee Randy Foye; and (the fictional) Dr. No, who in Ian Fleming’s same-titled novel survives an assassination attempt by being stabbed in the left—and therefore wrong—side of the chest.

Medical literature shows that doctors have only been musing on situs inversus for 250 years, and on dextrocardia a century more (it was discovered in 1643). But a passage from The Bible might give some dextrocardiacs pause. It says that “a wise man’s heart is at his right hand; but a fool’s heart at his left” (Ecc. 10:2).