In developing an intact rat model for myocardial ischemia using hyperpolarized 13C pyruvate, different compound formulations were evaluated. Infusion of 4-hydroxy-TEMPO-polarized sodium [1-13C]pyruvate was compared to an equivalent dose of buffered trityl radical-polarized [1-13C]pyruvic acid. Whereas higher levels of polarization and MRS signal were obtained with trityl radical, the metabolite signals normalized to total signal were lower. In particular, [1-13C]lactate signal relative to total signal was markedly higher using TEMPO-polarized pyruvate. [13C]bicarbonate and [1-13C]alanine signals were affected to a lesser degree. This study demonstrates the composition of the infused hyperpolarized pyruvate solution can significantly affect its metabolism in vivo.