Abstract: A compound of the formula, ##STR1## or its pharmaceutically acceptable salt, and its preparation process and pharmaceutical compositions characterized by containing these compounds as effective ingredients.These compounds have strong antithrombotic activity, cardiotonic activity, vasodilator activity and anti-SRS-A activity, and are useful as prophylactic or therapeutic agents for various thrombotic affections, congestive heart failure, hypertension, asthma, immediate type allergy diseases and the like.

Abstract: A 3(2H)pyridazinone of the formula: ##STR1## wherein R.sub.1 is C.sub.2 -C.sub.5 alkyl; R.sub.2 is hydrogen, C.sub.1 -C.sub.3 alkyl, chlorine or bromine; R.sub.3 is hydrogen or C.sub.1 -C.sub.4 alkyl; and each of Y.sub.1, Y.sub.2 and Y.sub.3 which may be the same or different, is hydrogen, C.sub.1 -C.sub.8 alkyl, C.sub.2 -C.sub.8 alkenyl, halogen, --(CH.sub.2).sub.l A [wherein A is substituted amino of the formula --N(R.sub.4) (R.sub.5) (wherein each of R.sub.4 and R.sub.5 which may be the same or different, is C.sub.1 -C.sub.4 alkyl, or R.sub.4 and R.sub.5 together form C.sub.4 -C.sub.6 alkylene), morpholino, 4-R.sub.6 -piperazin-1-yl (wherein R.sub.6 is C.sub.1 -C.sub.3 alkyl) or --OR.sub.7 (wherein R.sub.7 is hydrogen or C.sub.1 -C.sub.3 alkyl), and l is an integer of 0 to 3], --OR.sub.8 [wherein R.sub.8 is hydrogen, C.sub.1 -C.sub.8 alkyl, C.sub.3 -C.sub.5 alkenyl, benzyl or --(CH.sub.2).sub.q --R.sub.9 [wherein R.sub.9 is CO.sub.2 R.sub.3 (wherein R.sub.3 is as defined above), --CONHR.sub.3 (wherein R.

Abstract: A 3(2H)pyridazinone of the formula: ##STR1## wherein R.sub.1 is hydrogen, 2-propenyl, or straight chained or branched C.sub.1 -C.sub.4 alkyl; each of R.sub.2 and R.sub.3 which may be the same or different, is hydrogen, or straight chained or branched C.sub.1 -C.sub.3 alkyl; X is chlorine, or bromine; Y is hydrogen, halogen, nitro, amino, or --AR.sub.4 wherein A is oxygen, or sulfur, and R.sub.4 is hydroen, straight chained, branched or cyclic C.sub.1 -C.sub.8 alkyl, ##STR2## wherein R.sub.5 is hydrogen, or straight chained or branched C.sub.1 -C.sub.4 alkyl; and Ar is ##STR3## wherein each Z.sub.1 and Z.sub.2 which may be the same or different, is hydrogen, halogen, straight or branched C.sub.1 -C.sub.4 alkyl, or --OR.sub.6 wherein R.sub.6 is straight or branched C.sub.1 -C.sub.4 alkyl, and B is oxygen, sulfur, or --N.dbd.C-- (to form a quinoline or pyridine ring); or a pharamaceutically acceptable salt thereof.

Abstract: A 3(2H)pyridazinone of the formula: ##STR1## wherein R.sub.1 is hydrogen, 2-propenyl or straight chained or branched C.sub.1 -C.sub.4 alkyl; R.sub.2 is hydrogen or C.sub.1 -C.sub.3 alkyl; X is chlorine or bromine; Y is hydrogen, nitro, -NHR.sub.3 wherein R.sub.3 is hydrogen or straight chained or branched C.sub.1 -C.sub.4 alkyl, -AR.sub.4 wherein A is oxygen or sulfur and R.sub.4 is hydrogen, straight chained or branched C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.6 alkenyl having one double bond, C.sub.3 -C.sub.6 alkynyl having one triple bond, phenyl or ##STR2## wherein R.sub.5 is hydrogen or C.sub.1 -C.sub.4 alkyl, or halogen; Z.sub.1 is hydrogen, C.sub.1 -C.sub.4 alkyl, -OR.sub.6 wherein R.sub.6 is hydrogen, straight chained or branched C.sub.1 -C.sub.8 alkyl or ##STR3## wherein n is an integer of from 1 to 4, -N(R.sub.7).sub.2 wherein R.sub.7 is C.sub.1 -C.sub.4 alkyl, or halogen; Z.sub.2 is C.sub.1 -C.sub.4 alkyl, -OR.sub.6 wherein R.sub.6 is as defined above, -N(R.sub.7).sub.2 wherein R.sub.

Abstract: A 3(2H)pyridazinone of the formula: ##STR1## wherein R.sub.1 is hydrogen, methyl, C.sub.3 -C.sub.6 alkenyl, C.sub.5 or C.sub.6 cycloalkyl, benzyl, phenyl, --(CH.sub.2).sub.m CO.sub.2 R.sub.3 (wherein R.sub.3 is hydrogen or C.sub.1 -C.sub.5 alkyl, and m is an integer of from 1 to 4), --(CH.sub.2).sub.n A (wherein A is --OH or --N(R.sub.4).sub.2 wherein R.sub.4 is C.sub.1 -C.sub.3 alkyl, and n is an integer of from 2 to 6) or --CH.sub.2 CF.sub.3 ; R.sub.2 is chlorine or bromine; each of Y.sub.1 and Y.sub.2 which may be the same or different, is hydrogen, C.sub.1 -C.sub.5 alkyl, C.sub.2 -C.sub.8 alkenyl, halogen, --OR.sub.5 (wherein R.sub.5 is hydrogen, C.sub.1 -C.sub.8 alkyl or ##STR2## wherein q is an integer of from 1 to 4), --CO.sub.2 R.sub.6 (wherein R.sub.6 is hydrogen or C.sub.1 -C.sub.5 alkyl), --N(R.sub.7).sub.2 (wherein R.sub.7 is C.sub.1 -C.sub.4 alkyl) or --SR.sub.8 (wherein R.sub.8 is C.sub.1 -C.sub.4 alkyl); and Y.sub.3 is C.sub.1 -C.sub.5 alkyl, C.sub.2 -C.sub.8 alkenyl, halogen, --OR.sub.

Abstract: A 3(2H)pyridazinone of the formula: ##STR1## wherein R.sub.1 is hydrogen or C.sub.1 -C.sub.5 alkyl; R.sub.2 is hydrogen, C.sub.1 -C.sub.8 alkyl, chlorine or bromine; A is --NR.sub.3 -- or --O--; X is --(CH.sub.2).sub.n --, --CH(OR.sub.4)--, --CO-- or a single bond; when X is --(CH.sub.2).sub.n -- or a single bond, B is --O--, --S--, --NH--, --OSO.sub.2 --, or --OCO-- or a single bond, when X is --CH(OR.sub.4)--, B is --O--, --S--, --NH-- or --OSO.sub.2 --, and when X is --CO--, B is --O-- or --S--; and each of Y.sub.1, Y.sub.2 and Y.sub.3 which may be the same or different, is hydrogen, C.sub.1 -C.sub.8 alkyl, C.sub.2 -C.sub.8 alkenyl, halogen, ##STR2## or two of Y.sub.1, Y.sub.2 and Y.sub.3 together form ##STR3## and a pharmaceutically acceptable salt thereof.