Estimation of the extent of regional ischemia by scintigraphic methods has been hampered by the geometric constraints of two-dimensional imaging. Myocardial perfusion scintigraphy was performed using the Fresnel zone-plate tomographic camera after the injection of Tc-99m microspheres (20-40 micron) into a coronary artery. Coronary artery occlusion was performed in six dogs by embolization via a catheter guidewire system. Twenty milicuries of Tc-99m microspheres were injected into the left main coronary artery of the six occluded and three unoccluded dogs. Scintigraphy was performed in multiple projections in the living animal. Optical reconstruction of the holographic image provided tomographic gamma images of the heart. Scintigraphy was also performed with an Anger camera for comparison. The extent of the perfusion defect was measured by planimetry and expressed as a percentage of the ventricular area in that projection. The average of the right and left anterior oblique projections provided the most accurate estimate of the size of the perfusion defect (average error: 13.6%; range: 0-38.2%). Fresnel zone-plate imaging provided an accurate in vivo assessment of the extent of altered myocardial perfusion.