The invention provides a new use of landiolol hydrochloride in the treatment of a subject suffering from tachycardia or tachyarrhythmia, wherein landiolol-hydrochloride is administered for a period of at least 0.5 hours and up to at least 2 days, wherein the heart rate of said patient is persistently reduced during the administration period compared to the heart rate before treatment and no overshooting effect occurs after termination of said administration.
