OBJECTIVE To report the outcome of doxorubicin‐based chemotherapy as the sole treatment for dogs with echocardiographically identified right atrial masses and pericardial effusion. METHODS A retrospective study of case records of dogs with right atrial masses treated with doxorubicin. Dogs were excluded from the study if they had any type of surgery performed such as pericardiectomy or right atrial mass resection, or if their chemotherapy protocol did not include doxorubicin. The data collected included signalment, history, physical examination findings, diagnostic test results and long‐term survival. RESULTS Dogs with right atrial masses and pericardial effusion that received doxorubicin‐based chemotherapy alone had a median survival of 139 · 5 days (range 2 to 302 days). Chemotherapy side effects were frequent but mild. CLINICAL SIGNIFICANCE Doxorubicin‐based chemotherapy alone appears to be a viable treatment option for dogs with echocardiographically identified right atrial masses and pericardial effusion.