Introduction. Cor triatriatum is a rare congenital heart disease found incidentally in children. Although cor triatriatum can be an incidental finding in asymptomatic adults; it is extremely rare to find elderly patients without symptoms and is unique in a long distance runner. Case Presentation. We present the case of an 83-year-old long-distance runner with cor triatriatum sinistrum and atrial fibrillation who continues to be asymptomatic and has continued to run long distances, retaining his excellent functional capacity. Conclusion. Cor triatriatum sinistrum is a rare congenital disease, which is often found incidentally in children. Although it is also seen in adults without symptoms at normal exertion, it is rare to have this condition in long-distance runners especially in elderly people with other structural heart disease, that is, atrial fibrillation and mitral regurgitation.