To test the hypothesis that there arc discrepancies between 201T1− and 123I-β-methylpentadecanoic acid (BMIPP) distribution in the left ventricular myocardium and to assess whether BMIPP is a useful tracer agent for the assessment of left ventricular function in hypertrophic cardiomyopathy (HCM), myocardial single photon emission computed tomography (SPRCT) was performed with 201T1 and BMIPP in five normal subjects and 12 patients with asymmetric septal hypertrophy. Tracer uptake in the left ventricular myocardium was scored using a four-point grading System. A homogenous distribution of the tracer with no discrepancy between 201T1 and BMIPP uptake in the left ventricular myocardium was observed in each normal subject. In contrast, BMIPP uptake was reduced compared to 201T1 in 58 segments (40%) of the 144 myocardial segments in patients with HCM. Such discordant BMIPP uptake was observed in 15 segments (42%) of the septal segments, in 19 segments (53%) of the anterior segments, in eight segments (22%) of the lateral segments, and in 16 segments (44%) of the inferior segments. There was no significant correlation between 201T1 perfusion score and left ventricular ejection fraction, whereas there was a significant correlation between BMIPP perfusion score and left ventricular ejection fraction (r = 0.748; P <0.01). The results indicated that there were discrepancies between 201T1 and BMIPP uptake in a significant proportion of myocardial segments, suggesting the impairment of fatty acid metabolism and that BMIPP is a useful tracer agent for the assessment of left ventricular function in hypertrophic cardiomyopathy.