The hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) in the reaction ATP + H20 ⇌ ADP + Pi (inorganic phosphate) is used to drive all cellular processes, including those involved in ventricular contraction and relaxation. When spectral quality is sufficient to quantify the Pi peak, it is possible to assess the ratio of Pi to phosphocreatine (Pi/PCr), which is an established measure of the muscle control of energy production. It is also possible to assess cardiac intracellular pH from the Pi to PCr frequency offset. Most human cardiac 31P-MRS studies report only the PCr/ATP ratio, and are typically unable to quantify cardiac Pi because of partially overlapping resonances from 2,3-diphosphoglycerate in blood. We aimed to use ultra-high (7T) field strength and a novel 31P STEAM sequence to 1) non-invasively measure myocardial Pi/PCr and pH at rest and 2) for the first time record these parameters during catecholamine stress.