PHTHALAZINE DERIVATIVES

1-Piperidino-6,7-dialkoxy-phthalazine derivs. of formula (I), their acid addition salts and bioprecursors are new as the separate isomers or their mixtures. In (I), R is lower alkyl; Y is joined to the piperidino ring in position 3 or 4 and =-X-(CHR1)m-Z; R1=H or lower alkyl; m=1 or 2 with the condition that when m=2 then the two R1 groups may be identical or different; X=O or a bond with the condition that when m=1 then X= a direct bond; Z= -OOCNR4R5, -OOCR3, -N(R2)-CO-R3, -N(R2)-SO2-R3, -N(R2)-CO-NR4R5 or -N(R2)-COOR3; R2=H or lower alkyl; R3=lower alkyl, phenethyl, benzyl, phenyl or 2-, 3- or 4-pyridyl and R4, R5 independently=H or an R3 group. Lower group = =6C atoms pref. =4C atoms and are opt. branched. (I) phosphodiesterase inhibitors and cardiac stimulants which selectively increase myocardial contraction force without accelerating cardiac rhythm. They are used therapeutically or prophylactically for the treatment of cardiac insufficiency, in daily oral doses of 20mg-1g as 2-4 unit doses or in the case of acute cardiac insufficiency they are administered intravenously in doses of 1-300mg.