In an attempt to evaluate the possible usefulness of transmission computed tomography, CT scans of the chest of a series of dead dogs were obtained by means of an EMI body scanner. The sections thus obtained with and without the injection of contrast material reveal a great deal of cardiac morphology. Infarcts of the heart produced prior to scanning were imaged as regions of lower x-ray attenuation. The hearts of a series of live dogs following infarction were imaged by means of a positron emission transverse tomomograph (PETT) following administration of C-palmitate. The images permitted assessment of the relative size of the infarct. The relative advantages of transmission and emission tomography in cardiac visualization are discussed.