In 1970s Thailand a woman sentenced to death survived a firing squad aimed at the left side of her chest because her heart was on the right. This episode explains situs inversus, found in about 1 in 10,000 people, in which the internal organs are mirrored. In the total form the heart sits on the right, the liver and gallbladder on the left, the stomach and spleen on the right, and even the lungs swap their three and two lobes. Because the organs still connect correctly, most people are healthy: NBA player Randy Foye, Donny Osmond and Catherine O’Hara all have it, and Rose Marie Bentley of Oregon lived to 99 without knowing.

The cause traces to weeks four to six of gestation, when cilia on the embryo sweep fluid leftward to set the body’s axis. When they fail, as in primary ciliary dyskinesia, organ placement becomes a 50/50 coin flip. The hosts cover Kartagener syndrome, the dangers of partial reversals such as isolated levocardia and heterotaxy, how surgeons fit a standard donor heart into a mirrored chest, and an unexpected rise in cases in China after a COVID-19 wave.

• Appendicitis in a mirrored patient causes pain in the lower left abdomen, which can mislead doctors
• Isolated levocardia, about 1 in 2 million, carries a 95 percent rate of severe congenital heart disease
• Surgeons build baffles from synthetic grafts or the patient’s own pericardium to route blood into a donor heart
• A 2004 study found normal rates of left handedness, but a 2023 replication found 26 percent against 10.6 percent in the general population
• The China cases followed maternal infections during the four to six week window when cilia set organ placement