Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a primary heart muscle disease characterized structurally by progressive fibrofatty replacement of the right ventricle and clinically by life-threatening ventricular arrhythmias with left bundle branch block morphology. Recently, there has been a great deal of interest on ARVC/D as a cause of sudden death in young people, and it has been reported as the most common cause of exercise-related sudden death among competitive athletes in Italy. An autosomic dominant familial occurrence has been recognized, and four disease-causing genes have been recently identified in the dominant forms: ryanodinic cardiac receptor 2, desmoplakin, plakophilin 2, and transforming growth factor (TGF)-beta3. Furthermore, plakoglobin has been identified as the first gene responsible for the recessive variant of ARVC/D associated with palmoplantar keratosis and woolly hair (Naxos disease). However, although much progress has been made in molecular genetics, up to today, the pathogenesis of the disease is still unclear. The occurrence of myocyte apoptosis has been documented, suggesting that recurrent bouts of apoptosis may account for progressive atrophy of the myocardium, which is then replaced by fibrofatty tissue. Considering the frequent finding of myocarditis at histology, an inflammatory theory has been advanced, and infective mechanisms have been postulated to contribute to the onset and the progression of the disease. Cardiotropic viruses have been detected in some ARVC/D cases, and they have been proposed as possible etiologic agents. Several etiopathogenetic theories are herein presented in detail with particular attention to the inflammatory/infective one and its possible links between this and the genetic/dystrophic theories are discussed.