(edited to add further explanation and diagram)
The heart is pretty complex! And although I try and explain Nate's heart in pretty basic terminology, it still can be pretty confusing. Here are a couple of pictures that might help make it more clear!
Congenitally corrected transposition of the great arteries (CCTGA) is a pretty rare heart defect in which the heart’s lower half is reversed. Of all babies born with a heart condition, approx. 0.5% - 1% have CCTGA. It is also called L-TGA. It is different from and much less common than “regular” transposition of the great arteries (TGA or D-TGA).
To understand CCTGA, it helps to first understand how a normal heart works. We're going back to Grade 9 Bio here! A normal heart is divided into two sides. The right side pumps blood from the body into the lungs. The left side pumps the blood from the lungs out to the body. Each side has an atrium and a ventricle.The atrium acts like a “waiting room” for the blood. The ventricle does the hard work of pushing the blood out to the lungs or body. At the entrance and exit from each ventricle is a valve, which acts like a door. These valves allow the ventricle to fill with blood from one side, and then push it out the other. Each ventricle and valve is designed to do its specific job. The right ventricle is designed to give the blood a gentle push to send it to the lungs. It is bigger than the left ventricle and does not have as much muscle. The left ventricle is designed to give the blood a strong push out to the body. It has less space inside because its thick walls take up more space. The valve between the left atrium and ventricle, the mitral valve, is the body’s strongest valve. It is designed to stay shut against the strong push of the blood out to the body.
In CCTGA, the two ventricles are reversed. The two valves "follow' the ventricles, so they are also reversed. The weaker, larger right ventricle grows on your heart’s left side. It now has to do the job of the stronger ventricle and pump the blood to your body. Your stronger, smaller left ventricle grows on your heart’s right side. It pumps blood to the lungs. Because it's the strong one, it's pumping with more pressure than is required to get to the lungs. And the body’s weakest valve—the tricuspid valve,serves as the mitral valve, which in most cases, Nate's included, is very leaky — and has to deal with the high pressure blood being pumped through.
edited to add:
Although the two heart valves and two arteries are transposed or exit from the 'wrong' ventricle, the blood flows to the correct place because the ventricles are also reversed. And that's why it's called corrected....2 wrongs kinda make a right!
Clear as mud? Don worry, there won't be a test!!