BACKGROUND AND OBJECTIVES: Exercise myocardial perfusion scans in patients with hypertrophic cardiomyopa-thy have shown reversible perfusion abnormalities with unknown clinical significance. We performed this study to characterize dipyridamole Tl-201 SPECT imaging and correlate with clinical findings in patients with hyper-trophic cardiomyopathy. METHODS: Tl-201 SPECT was performed in 25 patients of hypertrophic cardiomyopa-thy with asymmetric septal hypertrophy and 20 normal controls after dipyridamole infusion (0.56 mg/kg). Myocardial wall was divided into 8 segments. Tl-201 uptake and relative washout rate were calculated. RESULTS: Tl-201 SPECT showed significantly lower Tl-201 uptake in basal septal (81.3+/-3.4% vs 78.2+/-6.4%, p<0.05) and apical septal wall on stress (88.2+/-4.7% vs 83.9+/-6.5%, p<0.05) and higher apical septal (86.6+/-5.2% vs 89.2+/-3.1%, p<0.05) and apical anterior wall uptake (88.7%+/-4.0% vs 91.4+/-4.9%, p<0.05) on redistribution images in patients with hypertrophic cardiomyopathy. Basal lateral wall uptake of hypertrophic cardiomyopathy was significantly lower than normal control on both stress (84.7+/-3.5% vs 81.2+/-7.3%, p<0.05) and redistribution images (85.0+/-5.8% vs 76.8+/-7.2%, p<0.0001). The septum/lateral uptake ratio of patients on rest image was significantly higher than that of normal controls (0.98+/-0.07 vs 1.07+/-0.10, p<0.001). There was no difference in age, sex, symptom, cardiac medication and the parameters of 2D-echo including left ven-tricular outflow obstruction between subgroups of normal vs abnormal washout in patients with hypertrophic cardiomyopathy. CONCLUSION: Dipyridamole Tl-201 myocardial SPECT shows reduced coronary vasodilatory capacity of myocardium, especially septum in patients with hypertrophic cardiomyopathy. High septal/lateral uptake ratio on redistribution image may be a characteristic finding. However, no correlation between abnorm-al Tl-201 washout and clinical findings was observed.