The present invention relates, in part, to heat transfer compositions and methods that include (a) from about 65% to about 75% by weight of HFC-32; (b) from about 15% to about 35% by weight of a compound selected from unsaturated —CF3 terminated propenes, unsaturated —CF3 terminated butenes, and combinations of these; and (c) from greater than about 0% to less than about 10% by weight of CO2, provided that the amount of component (c) is effective to improve heating capacity of the composition and reduce the defrost cycle in refrigerant applications, as compared to compositions lacking this component.