Metformin improves cardiovascular outcomes in diabetes, but its mechanism of action is controversial. Recent evidence suggests that Metformin reduces gluconeogenesis by altering hepatic redox state. Whether Metformin also alters cardiac redox state and metabolism is unknown, in part because of the difficulty in measuring cardiac metabolism in vivo. Hyperpolarized [1-13C]pyruvate magnetic resonance spectroscopy can assess the redox coupled interconversion of pyruvate and lactate with spatial localization to the heart. We therefore used hyperpolarized [1-13C]pyruvate magnetic resonance spectroscopy to investigate the effects of acute and chronic metformin treatment upon cardiac and hepatic metabolism.