The invention provides a heat transfer composition comprising (i) a first component selected from trans-1 3 3 3-tetrafluoropropene (R- 1234ze(E)) cis-1 3 3 3-tetrafluoropropene (R-1234ze(Z)) and mixtures thereof； (ii) carbon dioxide (R-744)； and (iii) a third component selected from 2 3 3 3-tetrafluoropropene (R-1234yf) 3 3 3-trifluoropropene (R-1243zf) and mixtures thereof.
