The use of hyperpolarized 3-13C acetoacetate to probe in vivo cardiac ketone bodies metabolism was investigated. Preliminary results showed the successful detection of 1-13C citrate and 1-13C acetylcarnitine after hyperpolarized acetoacetate delivery. Specifically, a significant increase in citrate with a corresponding decrease in acetylcarnitine was observed in the rat heart in vivo after 24hrs of fasting.