Abstract A series of levosimendan analogues were designed and synthesized, employing the Friedel–Crafts reaction, hydrolysis, and cyclization from the key intermediate compound R (−)-6-(4-aminophenyl)-5-methyl-4, 5-dihydro-3 (2H)-pyridazinone, which was obtained from the starting material, acetanilide. These compounds, except 1b, exhibited potent anti- congestive heart failure activities, especially the compounds 1e and 1k, which showed ...