X-ray microanalytical techniques using wavelength dispersive (WDS) and energy dispersive spectrometry (EDS) indicate that Ca2+ is present in intramitochondrial granules which occur in myocardial cells following irreversible ischemic injury. Preliminary results using tissue prepared for routine electron microscopy suggest that the degree of calcium binding that occurs in the mitochondria increases with increased duration of ischemia. Free ions are leached out of the tissue during processing; hence, the role of ion redistribution in producing myocardial necrosis cannot be elicited from a study of this nature. However, with continued progress in the development of techniques of tissue preparation x-ray spectrometry may provide a means of assessing quantitative ion alterations that occur during ischemia.