The aim of this study was to report the prevalence of degenerative and early inflammatory lesions and to discuss some histological aspects of normal and pathological mitral valve leaflets in healthy, normally slaughtered pigs. Mitral valves were collected from 112, 6 month-old, pigs reared under different conditions. Histological examination revealed the presence of myxoid degeneration in 29.5% of the valves with no significantly different prevalence according to rearing conditions; fibrosis was present in 12.5%; inflammation (non-vegetative valvulitis) occurred in 20 (17.9%) macroscopically normal valves. No vegetative endocarditis could be observed. A significantly higher degree of inflammation was observed in valves affected by myxoid degeneration (P < 0.05) and Anitschkow cells were prevalent in all the pathological valves (P < 0.01). Capillaries were observed in a wide majority of the valves (86.5%), but small arterioles were related to fibrotic thickening of the leaflets (P < 0.01). The following conclusions are discussed: (1) environmental factors seem not to influence the prevalence of endocardiosis; (2) inflammatory foci in myxoid valves are a reaction to both abnormal friction and products of degraded collagen and extracellular matrix; (3) the authors consider the presence of capillaries in pig valves a normal finding whereas proliferation of the vessels occurs under pathological conditions; (4) non vegetative valvulitis can be related to the presence of vessels in the valve and may have a role in both infectious endocarditis and fibrosis; (5) Anitschkow cells are normally observed in pig valves and are not specifically related to pathological lesions.