A heat transfer tube and a heat exchanger incorporating at least one heat transfer tubes are provided. The heat transfer tube and the heat exchanger are configured to operate in both a heating mode and a cooling mode (e.g., to optimize the reversible function a heat pump). The heat transfer tube includes a tube body with an interior surface and an exterior surface. The tube body defining an outer diameter (Do) and a wall thickness (WT), wherein a ratio (WT/Do) the wall thickness (WT) to the outer diameter (Do) is between 0.061 and 0.071. The heat transfer tube includes a plurality of adjacent helical fins protruding circumferentially around the interior surface of the tube body, and at least one groove disposed between the plurality of adjacent helical fins. The configuration of the heat transfer tube(s) is optimal for the reversible function of the heat pump.