Triple-energy window (TEW) method is a simple and practical approach for correcting Compton scatter in single-photon emission tracer studies. The fraction of scatter correction, with a point source or 30 ml-syringe placed under the camera, was measured by the TEW method. The scatter fraction was 55% for 201Tl, 29% for 99mTc, 57% for 123I. Composite energy spectra were generated and separated by the TEW method. Combination of 99mTc and 201Tl was separated well, and 201Tl and 123I were separated within an error of 10%; whereas asymmetric photopeak energy window was necessary for separating 123I and 99mTc. By applying this method to myocardial SPECT study, the effect of scatter elimination was investigated in each myocardial wall by polar may and profile curve analysis. The effect of scatter was higher in the septum and the inferior wall. The count ratio relative to the anterior wall including scatter was 9% higher in 123I, 7-8% higher in 99mTc and 6% higher in 201Tl. Apparent count loss after scatter correction was 30% for 123I, 13% for 99mTc and 38% for 201Tl. Image contrast, as defined myocardium-to-left ventricular cavity count ratio, improved by scatter correction. Since the influence of Compton scatter was significant in cardiac planar and SPECT studies; the degree of scatter fraction should be kept in mind both in quantification and visual interpretation.