Agent for prophylaxis and treatment of heart diseases using a carbostyril derivative of formula:
wherein R 1 is H or CN, and R 2 and R 3 are each H, alkyl optionally substituted by OH, cycloalkyl, alkenyl, phenyl, phenylalkyl having optionally substituents of alkoxyalkoxy, halogen, alkoxy, N0 2 , alkyl, CN, alkylthio or alkylsulfinyl on phenyl ring and having optionally OH-substituent on alkyl moiety, phenylsulfonylalkyl having optionally alkoxy substituent on phenyl ring, phenylthioalkyl, phenylsulfinylalkyl having optionally substituents of halogen or alkoxy on phenyl ring, phenoxyalkyl having optionally substituents of halogen or alkoxy on phenyl ring, pyridylalkyl having optionally substituents of halogen or alkoxy on pyridine ring, thienylalkyl, benzoylalkyl, anilinothiocarbonyl, benzoyl, pyridyl, phenylalkenyl, or group of -A-NR 4 R 5 (R 4 and R 5 , are each alkyl or phenyl having optionally substituents of halogen or alkoxy on phenyl ring, and A is alkylene which may be interrupted with 0), and a salt thereof, and novel carbostyril derivatives, and pharmaceutical composition for prophylaxis and treatment of heart diseases containing said novel carbostyril derivative.