We recently reported that myocardial phosphoinositide (PI) metabolism can be visualised by 1-[1-11C]-butyryl-2-palmitoyl-rac-glycerol (11C-DAG) in rats with myocardial infarction (MI). Angiotensin II, the receptors for which are expressed predominantly in infarcted areas with active fibrogenesis rather than in non-infarcted regions, is involved in the upstream signalling systems of PI metabolism and plays an important role in the process of left ventricular (LV) remodelling after MI. We therefore hypothesised that the distribution of 11C-DAG after MI may be affected by the inhibition of angiotensin converting enzyme, which is one of the most important factors in the development of LV remodelling after MI. Rats were injected with 11C-DAG after 3 or 10 weeks of treatment with captopril or no treatment following coronary artery ligation, and quantitative autoradiography was performed. Cells occupying the infarcted region were identified by immunohistochemistry. Compared with untreated rats, treatment with captopril for 3 weeks after MI elicited a reduction in the 11C-DAG uptake in the infarcted region (P<0.05) but not in the non-infarcted region, and was associated with a 22% decrease in the heart weight/body weight ratio. The thallium-201 distribution in the infarcted area was similarly low in the rats with and rats without the 3-week captopril treatment after MI. Abundant macrophages and myofibroblasts occupied the infarcted area in both rats with and rats without the captopril treatment for 3 weeks after MI. The 11C-DAG radioactivity in the infarcted region in the untreated rats was lower 10 weeks after MI than 3 weeks after MI (P<0.01). This finding was in agreement with the results of immunohistochemistry demonstrating that the number and size of macrophages and myofibroblasts were remarkably reduced in rats 10 weeks after MI compared with 3 weeks after MI. Captopril treatment for 10 weeks after MI did not decrease the 11C-DAG radioactivity in the infarcted area further. These data suggest that 11C-DAG is useful for visually detecting regions with activated PI metabolism after MI, and that captopril reduces PI metabolism in the infarcted region in the relatively early phase of MI, which might contribute to the attenuation of ventricular remodelling.