A ready-to-use injectable, co-solvents (ternary mixture) pharmaceutical composition for the treatment of cardiac conditions and diagnosis applications, comprising methyl-3-[4-(2-hydroxy-3-isopropylamino)propoxy]phenylpropionate hydrochloride (Esmolol hydrochloride), a buffering agent, ethanol and propylene glycol. The ready-to-use injectable, co-solvents (ternary mixture) pharmaceutical composition is capable of being stored in a modified flexible plastic container that may be heat-sterilized without deformation and/or without having the integrity of the closure system being compromised. A method for the manufacture of the ready-to-use injectable, co-solvents (ternary mixture) pharmaceutical composition is also disclosed.