This study was attempted to survey on the prevalence of canine heartworm infection (Dirofilaria immitis) in the Incheon area in 2006. This study showed comparative infection rates of canine heartworm in conjunction with different geographic locations and rearing environments (i.e., indoor, outdoor or free roaming). In total, 24 dogs (6.0%) were D. immitis positive among a total of 400 tested dogs. The geographic distribution of detection rates was Nam-gu (2 dogs, 6.7%), Yeonsu-gu (1 dog, 3.0%), Namdonggu (5 dogs, 8.0%), Pupyoung-gu (4 dogs, 6.7%), Kanghwa-gun (8 dogs, 13.0%), and Onjin-gun (4 dogs, 11.1%). In addition, 4 dogs (2.0%) or 20 dogs (10.0%) were positive for D. immitis among 202 indoor dogs or 198 outdoor dogs including free roaming dogs, respectively, while 13 dogs (11.7%) were positive for D. immitis among 111 outdoor dogs excluding free roaming dogs. In the case of 87 free roaming dogs, 7 dogs (8.1%) among them were positive for D. immitis.