Dirofilariasis is a zoonotic disease with worldwide distribution transmitted by Aedes, Anopheles and Culex mosquitoes to animals and humans. The objective of the study was to evaluate the prevalence of the heartworm Dirofilaria immitis (Leidy, 1856) in the shelter "El perro feliz" in the Sucre canton, Ecuador during the year 2021 diagnosed by the thick drop method. A descriptive study was carried out, and a sampling of 100 apparently healthy dogs was carried out during the months of September and October 2020. The thick drop method with Wright staining was used for the microscopic observation of the parasite morphology. The data obtained were analyzed through the percentage method to determine the percentage of positive animals and the ꭓ2 test (Chi-square) of independence at 5% significance to identify the relationship between the variables (age, sex, genetic group, color coat and weig...