Single-photon emission computed tomography (ECT) was evaluated during myocardial studies in dogs. Acute anterior and posterior infarcts were imaged following injection of 99mTc-pyrophosphate or 201Tl. In most cases, tomographic delineation of infarct location and extent correlated with tissue sections. The 99mTc images were far superior to the 201Tl images. ECT improves delineation of tracer within the myocardium.