The clinical features of tropical and temperate zone endomyocardial fibrosis (EMF) are the same, allowing for certain regional, environmental and possibly genetic variations. For example, the seasonal incidence in rainy humid areas probably reflects the large and repeated parasitic infestations in tropical EMF, while the absence of tissue eosinophilia in organs other than the heart in tropical EMF may reflect racial and environmental differences between tropical and western geographical areas that have still to be elucidated. That EMF occurs in Europeans who have lived in the tropics is undoubted, but the absence of right ventricular involvement in Europeans in the tropics, but not in temperate climes, is unexplained; perhaps it is a chance finding. It is also apparent that the extreme degrees of right ventricular EMF that are commonly seen in the tropics, with almost complete obliteration of the ventricular cavity are not usually seen in eosinophilic EMF in temperate areas. Involvement of both ventricles and of both atrioventricular valves is, however, common both in the tropics and in temperate climate EMF.