It is generally accepted that the risk of pulmonary thromboembolism, as consequence of successful heartworm adulticide therapy, is related to the degree of pulmonary arterial disease present at the time of treatment and to the size of the worm burden. Post-adulticide pulmonary thromboembolic complica-tions are most likely to occur in dogs when the arterial disease is extensive and/or the worm burden is high. In selected high-risk cases, an alternative to adulticide treatment (symptomatic or surgical) maybe chosen. The pre-treatment evaluation of a heartworm infected dog should therefore include the evaluation of both pulmonary disease and worm burden. While thoracic radiography isa sensitive tool for the detection of pulmonary, arterial and parenchymal disease, used alone, it is not a reliable method for evaluating worm burden. However, the combination of semi-quantitative antigen tests, echocardiographic visual-ization of worms and thoracic radiography may provide a more accurate estimate. The purpose of this study was to assess the relative utility of echocardiography, radiography, semiquantitative antigen testing and microfilariae counts to predict adult heartworm burdens in naturally infected dogs, and to determine whether or not a relationship existed between the number of heartworms present and the age of dogs present in the same environment for at least one year's exposure to infection.

A rescue kennel for stray dogs located in the province of Pavia (Po river valley, a hyperendemic area for heartworm disease in Northern Italy) was chosen for the study. One hundred and twenty three dogs lived in this kennel. While residents of the kennel none of them ever received heartworm preventative treatment due to economic limitations. Only heartworm-infected dogs that had been