What is Myxoma Disease? Myxoma is located on the left side of the heart. Left atrial myxomas are usually located in the septum (heart wall) region between the two atria, which prevents clean and dirty blood from mixing. The mass located in the heart wall is connected to the septum by a stalk. It does not move around, but it is mobile. If it has a loose structure, it passes from the left atrium of the heart through the mitral valve and...