Hydatid disease is medically and economically one of the most important of the zoonoses. There are four currently recognized species of Echinococcus: E. granulosus, E. multilocularis, E. vogeli and E. oligarthrus. The first three are commonly found in humans but E. oligarthrus had been recorded previously on one occasion only in the eye of a Venezuelan woman. Thus, I read with interest the recent paper by D'Alessandro and others which reviewed an earlier published case of hydatid disease in the heart of a Brazilian person who died of tetanus. Originally the case was described as being due to Echinococcus granulosus but this later paper considers that the infection was caused by E. oligarthrus and thus is the second reported human infection due to this species. As with the Venezuelan patient, both the cysts recovered from the Brazilian were unilocular—typical of E. granulosus, but untypical of E. vogeli and E. oligarthrus which are generally polycystic in nature—and diagnosis was based mainly on the morphological features of the hooklets of the protoscolex.