Technetium-99m tetrofosmin is a new myocardial perfusion imaging agent that accumulates rapidly and shows slow clearance from the myocardium. Dynamic acquisition and SPECT imaging were performed in a total of 26 patients. Using exercise-rest protocol, the single-photon emission computed tomography (SPECT) findings of 130 myocardial segments were classified as infarction, ischemia and partial filling and compared to those with 201Tl. Complete concordance of findings was obtained in 108 segments (83%) between images with 99mTc tetrofosmin and 201Tl. Partial filling was observed in 24 segments with 201Tl and 14 segments with tetrofosmin, showing a greater number of ischemic regions in 201Tl. However, in comparison with coronary arteriography (n = 19), overall sensitivity and specificity for detecting coronary artery stenosis (> or = 75%) was 15 of 25 (0.60) and 27 of 32 (0.84), respectively, which did not differ significantly from those of 201Tl, which was 18 of 25 (0.72) and 27 of 32 (0.84), respectively. Graphic analysis that assumes unidirectional transfer of the tracer was applied to initial dynamic changes and uptake constant k and distribution volume V were computed. Multiple vessel disease and congestive heart failure showed a low perfusion index (k/V), and may be used in this type of tracer with unidirectional uptake. This preliminary study in the clinical trial showed the usefulness of 99mTc tetrofosmin as a myocardial perfusion imaging agent.