Phosphorus magnetic resonance spectroscopy (³¹P‐MRS) has revealed a lot about the biochemistry of physiological and pathological processes in the heart. Nevertheless, until today, cardiac ³¹P‐MRS has not had any clinical impact, albeit some pioneering studies demonstrated that ³¹P‐MRS can indeed provide diagnostic information. In this paper, the development of techniques for human cardiac ³¹P‐MRS over the past decade is reviewed, and the requirements for a reliable clinical measurement protocol are discussed. Spatial localization with optimal pointspread function (SLOOP) is a new method to achieve spatial localization and absolute quantitation. Its properties are detailed, and preliminary findings in patients with dilated cardiomyopathy or myocardial infarction are presented. J. Magn. Reson. Imaging 2001;13:521–527. © 2001 Wiley‐Liss, Inc.