The human heart, stomach, and spleen lie on the left side of the body. At least, usually they do. One in ten thousand people (by current estimates), in fact, do not have their organs arranged that way. Their hearts lie on the right, their liver on the left. It’s a condition called situs inversus totalis (Latin, roughly meaning “totally reversed position”).
Many learn about their condition only when examined due to a medical concern. If no medical concerns arise, there’s no reason to find out. So, the actual number of those affected could be much higher than one in ten thousand. Especially seeing as it is uncommon for a total reversal of internal organs to cause health problems.
There are two causes known for the condition. Genetically, the trait can be passed on but only 1 in 4 children will have it active (autosomal recessive pattern). Also, if a fertilized egg splits to create twins, but comparatively delayed (9-12 days into development), it can result in “Mirror Image Twins”. They are exactly that: twins who mirror each other’s appearance. The mirroring can range from something as simple as hair line, to every organ being reversed.
Though uncommon, 5-10% of those living with the condition also have congenital heart disease. In addition, transplanting a heart is very difficult. The problem lies in the shape of the heart: all the ventricles and vessels are reversed. This either limits any donors to those with the same condition or makes surgery much more difficult in pairing up all the vessels in mirror.
Even bigger concerns arise if not all the organs are mirrored. Some do not have a full reversal of their organs, which is called situs inversus incompletus. In cases such as this, congenital heart disease affects 95% of those with the condition. The reverse condition is also possible, with many health risks all its own, and it’s simply called dextrocardia. In the classic James Bond novel Dr. No by Ian Fleming, Dr. No describes surviving a direct shot to the chest because of dextrocardia.