Age-related changes in intracellular calcium ([Ca2+]i)-vasoreactivity coupling efficiency (i.e., perfusion pressure divided by [Ca2+]i) were studied in vitro in tail arteries of male, normotensive, WAG/Rij rats aged 6, 12, 24, or 30 mo; one-half of these were chronically treated with the angiotensin I-converting enzyme inhibitor (ACEI) perindopril (1 mg.kg-1.day-1 orally) from 6 mo onward. Arterial segments were perfused at a constant flow rate (perfusion pressure taken as an index of arterial tone) and loaded with the acetoxymethyl ester of fluorescent dye fura 2 (fura 2-AM). Increases in [Ca2+]i were measured simultaneously with vasoconstriction after stimulation with a depolarizing hyperkalemic solution or the agonists norepinephrine or serotonin. Age had no effect on increases in [Ca2+]i vasoconstrictor responses, or electromechanical coupling efficiency (hyperkalemic solution). Increases in [Ca2+]i after agonists were similar in all groups, but vasoconstrictor responses and pharmacomechanical coupling efficiency decreased with age. ACEI had no effect on vasoconstriction or [Ca2+]i signals. In conclusion, coupling efficiency after agonist stimulation decreased with age; ACEI had no effect on coupling efficiency.