Doxorubicin (DOX) cardiotoxicity is unpredictable and begins with the first dose of chemotherapy. This study aimed to obtain information about circulating microRNA of cancer patients in the early dose of DOX chemotherapy, who either did or did not develop cardiac abnormality after the completion of chemotherapy. Plasma of 20 patients treated for breast cancer with DOX-chemotherapy was analyzed using quantitative RT-PCR. Circulating microRNA profiles of patients with DOX cardiotoxicity were compared to microRNA profiles of patients without DOX cardiotoxicity by quantitative real-time PCR. Thirty-two microRNAs were significantly dysregulated in the patients with abnormal cardiac function. Functional analysis of the 32 miRNAs suggested association with cell death, cell cycle, and inflammation. We have identified a miRNA signature associated with early doses of DOX-based chemotherapy that may potentially predict later impairment of cardiac function in breast cancer patients. Our data lay a foundation for future studies to identify biomarkers for presymptomatic DOX-induced cardiotoxicity.