Zardaverine (6-(4-difluoromethoxy-3-methoxyphenyl)-3[2H]pyridazinone) is a dual-selective inhibitor of phosphodiesterase III/IV was developed as a potential therapeutic agent for asthma. Zardaverine has been shown to inhibit inflammatory cell function, human peripheral blood mononuclear cells (PBMC) and T-cell proliferation and exert a positive inotropic action on the heart muscle. In animals, zardaverine exhibits both bronchodilatory and anti-inflammatory activities. In order to study the efficacy and safety in man, Zardaverine has been tested in clinical trials for the treatment COPD and asthma. Zardaverine has a modest and short-lasting bronchodilatory effect in patients with asthma. However, due to its fast elimination, the development of zardaverine was terminated in 1991.