We synthesized various 4-[[3,4-(methylenedioxy)benzyl]amino]quinazolines substituted at the 5- to 8-positions and evaluated their inhibitory activities toward cyclic GMP phosphodiesterase (cGMP-PDE) from porcine aorta. Monosubstitution at the 6-position was essential for the inhibitory activity, and the preferred substituents were compact and hydrophobic: methoxy (3b, IC50 = 0.23 microM), methyl (3c, 0.10 microM), chloro (3d, 0.019 microM), thiomethyl (3f, 0.031 microM), and cyano (3p, 0.090 microM) groups. Compounds 3b-d,f,p lacked inhibitory activity toward other PDE isozymes (all IC50 values > 100 microM), and their relaxing activities in porcine coronary arteries were well correlated with the inhibitory activities toward cGMP-PDE (r = 0.88, p < 0.05). One of these compounds, 3b, elevated the intracellular cGMP level in isolated porcine coronary arteries without causing any change in the cAMP level. We consider that this series of compounds dilates coronary arteries via potent and specific inhibition of cGMP-PDE.