During 'routine' bone scanning with diphosphonates, 10 elderly men were noted to show prominent myocardial uptake of Tc-hydroxymethylene diphosphonate (HDP) consistently, but no heart activity was seen with Tc-methylene disphosphonate (MDP). None had evidence of recent myocardial injury and the uptake persisted over a period of many months. In some, myocardial uptake defects were noted, analogous to 201Tl- and Tc-methoxyisobutyl isonitrile (MIBI) scans postinfarction. The condition appears to be essentially benign but its aetiology remains obscure. We have not been able to identify its cause; presumably atherosclerosis is one factor.