The clinical picture of myocardial ischemia accompanying allergic reactions is defined in the cardiologic literature as Kounis syndrome (KS) or allergic angina/myocardial infarction. In PubMed, a search for "Kounis syndrome", "allergic angina" or "allergic myocardial infarction" retrieves more than 100 results (among case reports, case series and reviews), most of which are published in cardiology/internal medicine/emergency medicine journals. In allergologic literature, heart involvement during anaphylactic reactions is well documented, but Kounis syndrome is hardly mentioned. Single case reports and small case series of angina triggered by allergic reactions have been reported for many years, and involvement of histamine and others mast cell mediators in the pathogenesis of coronary spasm has long been hypothesized, but the existence of an allergic acute coronary syndrome (ACS) is still questioned in the allergologic scientific community. Putative mechanisms of an allergic acute coronary syndrome include coronary spasm or heart tissue-resident mast cell activation (precipitating coronary spasm or inducing plaque rupture and coronary or stent thrombosis) due to systemic increase of allergic mediators, or heart tissue-resident mast cell activation by local stimuli. Indeed, the pathogenic mechanism of an ACS after an allergic insult might be related to direct effects of mast cell mediators on the myocardium and the atherosclerotic plaque, or to exacerbation of preexisting disease by the hemodynamic stress of the acute allergic/anaphylactic reaction. Which of these mechanisms is most important is still unclear, and this review outlines current views in the cardiologic and allergologic literature.