['Trimetazidine, known as a metabolic modulator, is an anti-anginal drug used for treatment of stable coronary artery disease (CAD). It is proposed to act via modulation of cardiac metabolism, shifting the mitochondrial substrate utilization towards carbohydrates, thus increasing the efficiency of ATP production. This mechanism was recently challenged; however, these studies used indirect approaches and animal models, which made their conclusions questionable. The goal of the current study was to assess the effect of trimetazidine on mitochondrial substrate oxidation directly in left ventricular myocardium from CAD patients.', 'Mitochondrial fatty acid (palmitoylcarnitine) and carbohydrate (pyruvate) oxidation were measured in permeabilized left ventricular fibres obtained during coronary artery bypass grafting surgery from CAD patients, which either had trimetazidine included in their therapy (TMZ group) or not (Control).', 'There was no difference between the two groups in the oxidation of either palmitoylcarnitine or pyruvate, and in the ratio of carbohydrate to fatty acid oxidation. Activity and expression of pyruvate dehydrogenase, the key regulator of carbohydrate metabolism, were also not different. Lastly, acute in vitro exposure of myocardial tissue to different concentrations of trimetazidine did not affect myocardial oxidation of fatty acid.'] Does trimetazidine alter metabolic substrate oxidation in cardiac mitochondria of target patient population?