The effects of perindopril, 4 mg orally, on brachial artery blood flow and diameter (pulsed Doppler) and on forearm vascular resistance were investigated and compared in six normal subjects and 10 congestive heart failure patients (New York Heart Association class III or IV). Pre-drug values of brachial artery blood flow and diameter were significantly lower in patients with congestive heart failure than in normal subjects, the reverse being true for forearm vascular resistance. In normal subjects perindopril increased brachial artery blood flow and decreased forearm vascular resistance, while in patients with congestive heart failure the same effects were observed but they were more pronounced and brachial artery diameter was increased. In patients with congestive heart failure, when perindopril effects were maximal, brachial artery blood flow remained below the baseline values of normal subjects but brachial artery diameter was normalized. Finally, there was a correlation between the drug-induced decrease in forearm vascular resistance and basal plasma noradrenaline values in all subjects taken together. These results indicate that: (1) the renin-angiotensin system plays a major role in vasoconstriction in patients with congestive heart failure; (2) this vasoconstriction affects both large arteries and arterioles; (3) perindopril is able to considerably improve peripheral haemodynamics in congestive heart failure; and (4) this improvement is linked to the initial sympathetic tone.