Hearts from 12 patients, 82-92 ears old, with immunohistochemically verified pronounced senile systemic amyloidosis, were studied postmortem. Sections from the left ventricle, atrioventricular and sinus nodes and atrioventricular bundle were studied using the light microscope. The weights of the hearts varied between 310 and 870 grams. In the studied parts of the conduction system, the amounts of amyloid were considerably smaller than in the surrounding myocardium. Clinical data were taken from available case records. Eight of the patients had a history of uncomplicated congestive heart failure, but only two had been in hospital with cardiac symptoms prior to their last admission. The electrocardiogram showed atrial fibrillation in nine cases, left bundle branch block in three, right bundle branch block in two and left anterior hemiblock in one. No evidence of atrioventricular dissociation was seen and, in no case, was death considered to be due to conduction disturbances. Amyloidosis was a contributing cause of death in 7 patients, while the remaining patients died of other diseases. Amyloidosis is rarely diagnosed before death and was not suspected during life in any of our patients.