Three of nine siblings were affected by atrial standstill. Clinical, electrophysiological, and histological findings in two of these cases were studied. Electrophysiological studies showed persistent atrial standstill in one and partial atrial standstill in the other. Biopsy specimens of the right atria showed amyloid deposits, but specimens of the right ventricles and skin did not. Neither patient had peripheral neuropathy, gastrointestinal disorder, or renal dysfunction. Familial atrial standstill is usually associated with peripheral neuropathy. In the two cases studied amyloid deposition mainly affected the atrium, rather than the ventricles or other organs, and caused atrial standstill.