A study to determine the seroprevalence of Dirofilaria immitis was carried out in feral cats in Grenada. Of the 137 feral cats tested for circulating antibodies (IgG; lateral-flow immunoassay) and circulating antigens (Ag; enzyme-linked immunosorbent assay), 8% (95% confidence interval (CI) 3.5–12.5%) were antibody positive and 5.1% (95% CI 1.4–8.8%) were antigen positive. No significant difference between cats aged>1 to 4 years and cats less than 1 year of age was found (P>0.05, χ2). There was also no significant difference (P>0.05, χ2) between male and female cats. Dirofilaria immitis prevalence is relatively high in the feral cat population of Grenada. Evidence of D. immitis infection in feral cats coupled with the endemic nature of heartworm disease in dogs in Grenada leads us to suggest the introduction of heartworm prophylaxis in cats. To the authors' knowledge, this serological evidence of heartworm infection in feral cats in Grenada is the first report from the Caribbean region.