First degree atrioventricular block associated with right atrial myxoma.

First degree atrioventricular block occurred in a 68 year old man with a large right atrial myxoma. This conduction abnormality resolved within three months of successful surgical removal of the tumour. It is suggested that mechanical compression by the myxoma on either the underlying conduction tissue or the interventricular septum is likely to have caused this phenomenon.