Effect on contractility of skinned fibres from mammalian heart and smooth muscle by a new benzimidazole derivative, 4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazol-5-yl]-5-methy l-3(2H )- pyridazinone.

The positive inotropic drug 4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazol-5-yl]methyl-3(2 H)- pyridazinone (UD-CG 115 BS) enhances calcium induced contraction of skinned fibres from cardiac muscle probably by increasing the calcium sensitivity of troponin. Submaximal calcium induced contraction of skinned fibres from a smooth muscle (guinea-pig taenia coli) are slightly inhibited.