This study evaluates the feasibility of hyperpolarized 13C MRS for detection of early metabolic response in the myocardium of patients after anthracycline treatment. Patients with breast cancer were studied using hyperpolarized [1-13C]pyruvate before and after doxorubicin. Appearance of [13C]bicarbonate was significantly decreased after doxorubicin compared to the baseline exam while no change in [1-13C]lactate was detected. The reproducibility of hyperpolarized exams was examined by two injections of hyperpolarized [1-13C]pyruvate. The study demonstrates that hyperpolarized 13C spectra of the heart are sensitive to early injury of the mitochondria after doxorubicin therapy in patients with breast cancer in a reproducible manner.