Keith tells the judge Diane has an atrial myxoma and her heart is literally splitting in two. An atrial myxoma is a benign tumor in the top half of the heart, generally in the septum separating the left from the right atrium. The heart would not split in two although it may beat so irregularly or so inefficiently as to cause serious problems. The standard treatment is to surgically remove the tumor; a transplant would be very unusual.