Mastocytosis is characterised by clonal proliferation of mast cells in the skin and in various internal organs, and by symptoms related to an acute release of mast cell-derived mediators. In 20-30 % of patients, mastocytosis occurs without the typical skin lesions of urticaria pigmentosa that are usually the first clinical sign of the disease. In these patients, anaphylaxis is often the presenting sign of the disease. We report three cases in which a cardiac emergency (cardiac arrest or ventricular fibrillation) was the first clinical manifestation of anaphylaxis associated with systemic mastocytosis. All patients were men, none of them had previous episodes of anaphylaxis or other mediator-related symptoms, and none had major pre-existing cardiovascular condition. An eliciting factor was identified in one case (a wasp sting), but one was found in the other two. Elevation of the serum tryptase suggested a mastocytosis, which was confirmed by bone marrow biopsy. This case series demonstrates that cardiovascular emergencies may be presenting signs of mastocytosis, and that elevation of serum tryptase after an acute cardiac event, if confirmed under basal conditions, may be useful for diagnosing this disease.