For example, in a study performed on right atrial appendage tissues of atrial fibrillation (AF) and sinus rhythm patients matched with normal controls, not only did the AF patients have increased MCT1, but they also had increased oxidative stress and increased expression of mitochondrial apoptotic proteins (e.g. cytochrome c, cleaved caspases 3 and 9) [43]. This evidence concerns the gene CYCS and atrial fibrillation.