A heat sink for cooling at least one heat dissipating surface of an electric machine assembly; - said electric machine assembly further comprising a stator and a housing with plurality of surfaces; - said heat sink further comprising at least one substantially cylindrical wall with at least one surface area exposed to a cooling medium, - wherein said substantially cylindrical wall is at least partially adapted to be associated with at least one portion of said electric machine assembly; i - said substantially cylindrical wall further comprising a central longitudinal axis and at least one substantially cylindrical first surface in communication with said cooling medium; - said first surface further comprising at least one group of substantially parallel pin fin arrangement, - wherein said pin fins are extending from said first surface, and - wherein said pin fins are protruding away from said first surface, characterized in that - said first surface further being traversed by at least one cross section plane, - said cross section plane being perpendicular to said central longitudinal axis and defining a circular cross section area with said first cylindrical surface; - said circular cross section area further comprising at least one sector; - said sector further comprising a sector central angle (α), a bisector angle (α/2) formed by the angle bisector of the sector central angle (α) and being the half of the sector central angle (α), and a sector form release angle (β), - said sector central angle (α) being in the range between 18° and 180°, - the sector form release angle (β) being formed by the angle bisector of the sector central angle (α) and the pin fin axis of the respective pin fin intersecting the first surface, - the sector form release angle (β) being in the range between +45° and -45°, wherein 45° being the maximum value the bisector angle (α/2) can get; - a negative form release angle (β) representing a clockwise inclination of the pin fin axis, while a positive form release angle (β) representing an anticlockwise inclination of the pin fin axis, - said sector further comprising at least the at least one group of said substantially parallel pin fins on said first surface, - said pin fins being unidirectional and - at least two pin fins of said group of substantially parallel unidirectional pin fins in the sector are so located in the sector, that two significantly different angles are, each one, formed between the angle bisector of the sector central angle (α) and a radius, of the circular cross section area, joining the central axis with a corresponding intersection of the first surface with a respective pin fin, - the arrangement and inclination of said pin fins in relation to said first surface being according to said sector release angle (β) adapted to the required cooling medium flow regime. - said electric machine assembly further comprising a stator and a housing with plurality of surfaces; - said heat sink further comprising at least one substantially cylindrical wall with at least one surface area exposed to a cooling medium, - wherein said substantially cylindrical wall is at least partially adapted to be associated with at least one portion of said electric machine assembly; i - said substantially cylindrical wall further comprising a central longitudinal axis and at least one substantially cylindrical first surface in communication with said cooling medium; - said first surface further comprising at least one group of substantially parallel pin fin arrangement, - wherein said pin fins are extending from said first surface, and - wherein said pin fins are protruding away from said first surface, - said first surface further being traversed by at least one cross section plane, - said cross section plane being perpendicular to said central longitudinal axis and defining a circular cross section area with said first cylindrical surface; - said circular cross section area further comprising at least one sector; - said sector further comprising a sector central angle (α), a bisector angle (α/2) formed by the angle bisector of the sector central angle (α) and being the half of the sector central angle (α), and a sector form release angle (β), - said sector central angle (α) being in the range between 18° and 180°, - the sector form release angle (β) being formed by the angle bisector of the sector central angle (α) and the pin fin axis of the respective pin fin intersecting the first surface, - the sector form release angle (β) being in the range between +45° and -45°, wherein 45° being the maximum value the bisector angle (α/2) can get; - a negative form release angle (β) representing a clockwise inclination of the pin fin axis, while a positive form release angle (β) representing an anticlockwise inclination of the pin fin axis, - said sector further comprising at least the at least one group of said substantially parallel pin fins on said first surface, - said pin fins being unidirectional and - at least two pin fins of said group of substantially parallel unidirectional pin fins in the sector are so located in the sector, that two significantly different angles are, each one, formed between the angle bisector of the sector central angle (α) and a radius, of the circular cross section area, joining the central axis with a corresponding intersection of the first surface with a respective pin fin, - the arrangement and inclination of said pin fins in relation to said first surface being according to said sector release angle (β) adapted to the required cooling medium flow regime.