The purpose of this study was to compare the abdominal and arm areas in the patients using subcutaneous heparin in terms of pain, hematoma, and ecchymosis development. As a result of subcutaneous heparin injections, complications such as pain, ecchymosis, and hematoma may develop in the injection site. The injection site chosen for injection is one of the factors that are effective on complications. This quasi-experimental study was conducted with 54 patients at orthopedicstraumatology and cardiothoracic surgery clinics of a university hospital. The data were collected using a patient description and follow-up form, visual analog scale, transparent film, and a chronometer. Ecchymosis and hematoma were evaluated at the 48th hour after injection, whereas the pain level was evaluated right after the injection, and the pain duration was evaluated during the injection. The rate of pain in the arm area was statistically higher. Differences between the areas in terms of level and duration of pain and development and size of ecchymosis and hematoma were not significant. More pain developed due to heparin injection in the arm area than in the abdominal area. No differences were observed between the areas in terms of level and duration of pain, development and size of ecchymosis, or development and size of hematoma.