More than 100,000 Americans die each year from fatal heart attacks. Whereas, coronary intensive care units have made significant progress in controlling potentially lethal arrhythmias, there has been no success in reversing cardiogenic shock. Methods proposed for treating patients with myocardial infarction or severe myocardial ischemia include early diagnosis and chemical or physical in-tervention measures designed to minimize the volume of the infarcted tissue. In order to evaluate these approaches, we seek new meth-ods for noninvasively quantitating the volume of the ischemic and infarcted myocardium. Some isotopes which localize in the healthy myocardium, and others which accumulate specifically in the ischemic myocardium, offer a sensitive noninvasive technique of following myocardial injury. However, simple two-dimensional imaging of the distribution of injected isotopes such as 43K, 81Rb, 201T1 for negative imaging, or 99mTc-tetracycline, 99mTc-pyrophosphate, or 203Hg-chlormerodrin for positive imaging, is not adequate for quantitative and definitive evaluation of the function of the myocardium. Gamma camera or rectilinear scanner images suffer from the fact that the isotope distribution throughout the entire thorax is projected onto a plane and the resulting poor contrast image repre-sents not only myocardial uptake, but appreciable uptake by skeletal muscle and adjacent soft tissues for negative agents such as 201T1; and uptake by the ribs and sternum for the positive agents such as 99mTc-pyrophos-phate. These problems can be circumvented by three-dimensional imaging techniques, and this paper is devoted to a discussion of three methods of imaging the three-dimensional dis-tribution of isotopes in the myocardium: (1) Three-dimensional imaging using multiple Angercamera views. (2) Longitudinal tomographic images with compensation for blurring. (3) Transverse-section reconstruction using coincidence detection of annihilation gammas from positron emitting isotopes.