Vehicle seat with variable backrest shape

The seat has a seat frame (11), a seat surface frame (12) and a backrest frame (13). The backrest frame has a left backrest longitudinal strut (15), a right backrest longitudinal strut (16), an upper cross beam (18) and a lower cross beam (17). The right and left backrest longitudinal struts are pivoted arranged at the seat frame, such that a backrest frame is deformed in a height direction.