[Systemic mastocytosis with myo-pericardial localization and atrioventricular block].

The case of a 46 year old man with systemic mastocytosis with myocardial and pericardial involvement confirmed histologically after open biopsy is reported. The patient presented with skin, bone and medullary lesions and, in addition, with atrioventricular block and pericardial effusion. The possible mechanisms of the atrioventricular conduction defect are examined in the light of the physiological role of the mastocyte and research into the action of histamine on the myocardium. In particular, the negative dromotropic effect of histamine and fibrosis formation related to the mastocyte's function of connective tissue regeneration are discussed. This case, though rare, should alert the clinician to the possibility of myocardial and pericardial involvement in patients with mastocytosis. Further study into the effects of histamine on myocardium under physiological and pathological conditions is required.