Myocardial uptake of 99Tcm-tetrofosmin in vivo is determined by a combination of flow and metabolic status of myocytes. The accumulation of tetrofosmin in the mitochondria is related to their ability to transduce metabolic energy into electronegative membrane potential. Trimetazidine (TMZ), an anti-ischaemic drug, appears to have a metabolic cytoprotective effect related to mitochondrial function, since it does not induce systemic or coronary haemodynamic changes. In this study, we evaluated the effects of TMZ on tetrofosmin uptake in hypoperfused myocardial regions in patients with coronary artery disease (CAD). Twenty-two patients, 14 with previous myocardial infarction (group A) and eight with a history of angina (group B), with angiographically documented CAD were studied. All patients underwent two tetrofosmin SPET studies at rest, before (baseline) and 1 week after TMZ administration (post-TMZ). On quantitative analysis, 131 segments showed less tetrofosmin uptake at baseline. In these segments, tetrofosmin uptake was 51 +/- 13% at baseline and 55 +/- 15% post-TMZ (P < 0.001 vs control). In the 86 hypoperfused segments of group A, tetrofosmin uptake was 48 +/- 14% at baseline and 52 +/- 17% post-TMZ (P < 0.001 vs control). In the 45 hypoperfused segments of group B, tetrofosmin uptake was 56 +/- 9% at baseline and 60 +/- 10% post-TMZ (P < 0.001 vs control). In the remaining 309 segments, no significant difference in tetrofosmin uptake before and after TMZ was observed. In conclusion, our results suggest that TMZ administration may increase myocardial uptake of tetrofosmin in hypoperfused regions at rest in patients with CAD, based on its metabolic effect.