To elucidate the mechanism of left ventricular dysfunction associated with left ventricular hypertrophy in hypertension, coronary blood flow (CBF) and left ventricular mass (LVM) were measured in 62 patients with essential hypertension (mean age, 54 +/- 13 years) and 22 normotensive control subjects (mean age, 57 +/- 13 years). According to the indicator fractionation principle, CBF/cardiac output (CO), estimated on the basis of the ratio of myocardial uptake/total injected dose of thallium-201 (% cardiac uptake), was measured. CBF and CBF per 100 g of myocardium (unit CBF) were calculated according to the following formulas: CBF=% cardiac uptake x CO, and unit CBF=(CBF/LVM) x 100, where CO and LVM are echocardiographically determined. Midwall fractional shortening (FS) and isovolumic relaxation time (IRT) were calculated as the indices of systolic and diastolic functions. CBF was greater in hypertensives than in controls (218.2 +/- 74.0 vs. 187.4 +/- 40.4 ml/min, p < 0.05), though unit CBF was smaller in hypertensives than in controls (99.1 +/- 22.0 vs. 141.2 +/- 31.6 ml/min/100 g, p < 0.0001). Multiple regression analyses showed that unit CBF was the most potent predictor of both midwall FS and IRT. A positive correlation was found between midwall FS and unit CBF (r=0.669, p < 0.0001), and a negative correlation between IRT and unit CBF (r=-0.579, p < 0.0001). In conclusion, myocardial ischemia reflected by the decrease in unit CBF may be closely related to left ventricular dysfunction in patients with essential hypertension.