An automatic pipette assembly for an isothermal titration micro calorimetry system, comprising a pipette housing, a syringe with a titration needle arranged to be inserted into a sample cell for supplying titrant, and a linear activator for driving a plunger in the syringe, the titration needle is rotatable with respect to the housing and is provided with a stirring paddle arranged to stir fluid in the sample cell, wherein the automatic pipette assembly comprises a stirring motor for driving the rotation of the titration needle. There is also provided an isothermal titration micro calorimetry system.