['The aim was to test the hypothesis that endothelium dependent vasomotor control is impaired in heart failure.', 'The haemodynamic effects of NG-nitro-L-arginine (NNA), an inhibitor of nitric oxide synthesis, were studied in five dogs with and without pacing induced heart failure.', 'In healthy dogs, NNA increased total peripheral resistance and arterial pressure, decreasing cardiac output and heart rate. These effects were partially reversed by L-arginine. In dogs with heart failure, NNA did not change any haemodynamic variable. However, L-arginine decreased total peripheral resistance.'] Is systemic vasoconstriction induced by inhibition of nitric oxide synthesis attenuated in conscious dogs with heart failure?