Fig. 3. Effect of SNAP (100 µmol l^-1), an NO donor, on cardiac muscle action potential duration (APD) in goldfish ventricle (N=8). Under normoxic conditions, APD₅₀ and APD₉₀ were significantly shortened upon 3 min exposure to SNAP. Inset shows a control action potential (left) and one recorded in the presence of SNAP (right, and superimposed at arrow). Values are means ± 1 S.E.M. ^*, significantly different from control (P<0.05).