Although the pathophysiology of microvascular angina is unclear, intracellular metabolic changes are believed to be the main factors. Trimetazidine has an intracellular metabolic effect in coronary insufficiency. The effect of trimetazidine in microvascular angina is unknown. Thirty-five patients (8 men, 27 women, age 36-57 years, mean 43.9 +/- 6.4 years) with microvascular angina were included in this study. The effects of trimetazidine (60 mg daily) were investigated in a placebo-controlled, double-blind study consisting of two 4-week treatment periods. Patients were assessed by symptom-limited exercise testing (Bruce protocol). Heart rate and systolic blood pressure at rest, peak exercise, and the time of 1 mm ST segment depression were not significantly different between placebo and trimetazidine treatment. Trimetazidine prolonged total exercise time and time to 1 mm ST depression compared with placebo. Maximum ST depression was less in patients with trimetazidine therapy than those with placebo. It is concluded that trimetazidine has a beneficial effect in cases with microvascular angina.