IN domestic carnivores, almost all parasitic diseases of the heart and lungs are caused by nematodes belonging to the Metastrongyloidea superfamily, which includes Angiostrongylus vasorum, Oslerus osleri, Filaroides species, Aelurostrongylus abstrusus and Crenosoma vulpis. The only exception is heartworm, which is caused by the filarial nematode Dirofilaria immitis. Metastrongyle infections are encountered throughout the UK, although certain geographical hot spots have been reported. While the incidence of disease associated with these parasites in dogs and cats is relatively low, largely due to the widespread use of prophylactic anthelmintics, there is anecdotal evidence that angiostrongylosis and Crenosoma infection, in particular, are on the increase. This may reflect the increasing urbanisation of the fox, which has the potential to act as a reservoir of infection. D immitis is not currently endemic in the UK and has been discussed in detail in a separate article on imported infectious diseases. This article reviews the metastrongyle infections of prime concern in this country and, for each parasite, discusses the diagnosis and management options.