To investigate the regional left ventricular (LV) contraction kinetics in patients with hypertrophic cardiomyopathy (HCM), we performed ECG gated myocardial tomography (gated-SPECT) with 99mTc methoxy-2-isobutyl isonitrile (MIBI) at rest in 11 patients with HCM and 13 normal subjects. In order to evaluate regional LV contraction kinetics, multi-plane long axial tomograms were constructed and LV was divided into 17 segments. From the time activity curve of myocardial count, percent change during systole (%CC) was calculated in each segment. Normal range of %CC in each segment was derived from normal files. Systolic asynchrony in each patient was expressed as SD (standard deviation) of R-wave to peak count (R-PC) intervals of 17 segments. Decreased %CC was observed in 87 of 187 segments (47%) in HCM (8 +/- 5 segments/patient, range; 2-14 segments/patient). SD in patients with HCM was significantly greater than that in normal subjects (5.9 +/- 1.3 vs. 3.5 +/- 0.6, p < 0.01). The extent of decreased %CC in patients with HCM correlated well with global 123I-BMIPP (BMIPP) uptake and the extent of regional abnormality of BMIPP (Defect Score) (r = -0.79, r = 0.88 each, p < 0.01). On the other hand, SD correlated well with left ventricular (LV) filling rate during early diastole (r = -0.66, p < 0.01). Patients with HCM were divided into 2 groups whether LV ejection fraction (EF) increased (Group 1) or decreased (Group 2) by exercise stress. SD in Group 2 was significantly greater than that in Group 1. In segments with decreased %CC, the distribution of R-PC interval was different with that in segments with normal %CC. These results suggested that indexes which were derived from gated-SPECT with MIBI could bring several informations which were important to assess the pathologic condition of HCM.