1. A method for obtaining of a solid composition comprising, by weight based on the total weight of the composition: (a) from 1 to 70% of an active ingredient based on metoprolol which is not in an amorphous form; (b) from 10 to 95% polyethylene oxide; (c) the balance consisting of conventional additives, comprising the steps consisting of: (i) mixing said active ingredient based on metoprolol and optionally one or several additives with aqueous solution for a sufficient time, and then (ii) adding polyethylene oxide and mixing for a sufficient time; 2. A method according Claim 1, wherein active ingredient based on metoprolol is metoprolol tartrate. 3. A method of Claim 1 or 2, wherein said composition comprises: (a) from 5 to 45% of an active ingredient based on metoprolol which is not in an amorphous form; (b) from 20 to 70% polyethylene oxide; (c) the balance consisting of conventional additives. 4. A method accordind to any of Claims 1 to 3, wherein polyethylene oxide has a molecular weight which varies from 50,000 to 8,000,000 and preferably from 300,000 to 3,000,000. 5. A method according to any of Claims 1 to 4, in which the balance consisting of conventional additives comprises microcrystalline cellulose, lactose, ascorbic acid, pigments, plasticizers, lubricants, etc. 6. A method according to any of Claims 1 to 5, in which (i) stage of mixing with aqueous solution is carried out in precense of liquid surplus. 7. A method according to any of Claims 1 to 6, additionally comprising granulation step. 8. A method according to Claim 7, in which said granulation step is carried out by passage through a suitable sieve. 9. A method according to Claim 7, in which said granulation step is carried out using granulator with air-fluidized bed. 10. A method according to any of Claims 1 to 9, additionally comprising drying step. 11. A method according to any of Claims 7, 9 or 10, wherein granulation and drying steps are combined, using granulator with air-fluidized bed. 12. A method according to any of Claims 1 to 11 additionally comprising pressing step. 13. A method according to Claim 7, in which said pressing step is preceded by the step of introduction of conventional additives and mixing. 14. A method according to any of Claims 1 to 13 comprising the following steps: (i) mixing for a sufficient time an active ingredient based on metoprolol, and optionally, one or several additives with aqueous solvent; then (ii) adding polyethylene oxide and mixing for a sufficient period of time; (iii) granulation the mixture obtained by step (ii); (iv) drying the granules thus formed for a sufficient period of time; (v) optionally adding one or more additives, with mixing in the dry state for a sufficient time; (vi) compressing the mixture obtained from the preceding step to obtain the desired compressed tablet. 15. A method according to Claim 14, in which (i) stage of mixing with aqueous solution is carried out in precense of liquid surplus. 16. A method according to Claims 14 or 15, wherein granulation and drying steps are combined, using granulator with air-fluidized bed. 17. A method according to any of Claims 1 to 13 comprising the following steps: (i) mixing for a sufficient time an active ingredient, and optionally, one or several additives with aqueous solvent; then (ii) granulation the mixture obtained by step (i); (iii) optionally drying the granules thus formed for a sufficient period of time; (iv) adding polyethylene oxide and optionally adding one or more additives, and mixing thereof for a sufficient time; (v) compressing the mixture obtained from the preceding step to obtain the desired compressed tablet. 18. A method according to Claim 17, wherein mixing, granulation and drying steps are combined, using granulator with air-fluidized bed. 19. A method according to any of Claims 1 to 18 wherein said aqueous solvent comprises water and optionally water-soluble additives. 20. A method according to Claim 19, wherein said aqueous solvent comprises water and sticker in the amount of up to 20%.