A self-propelled cart for transporting heavy loads of the type comprising: a chassis having, on top, a substantially horizontal loading deck on which the item to be transported rests; and a series of pivoting wheel assemblies that are located beneath the chassis, each with the capability of rotating, on command, about a respective reference axis; each pivoting wheel assembly comprising: a slewing bearing which is fixed to the chassis with the capability of rotating about said reference axis; a servo-motor which is adapted to rotate, on command, the slewing bearing about said reference axis; a horizontal axle which is located beneath the slewing bearing, is connected to the slewing bearing so as to rotate together with the latter, and is provided with at least two ground-resting wheels coaxial to one another; and an active suspension which is interposed between the horizontal axle and the slewing bearing, and is capable of varying, on command, the distance (d) between the plane on which the slewing bearing lies and rotates and the rotation axis of the two wheels; the horizontal axle of at least one of said pivoting wheel assemblies comprising: a central hub which extends between the two wheels of the axle coaxial to the wheel rotation axis and is laterally connected to the slewing bearing via a hinge that allows the central hub to swing about a first axis which is perpendicular to said reference axis and is parallel and spaced from the wheel rotation axis; and an engine adapted to drive into rotation the wheels of the axle about the common rotation axis; wherein the engine is located outside of the central hub, is arranged parallel to the wheel rotation axis, is spaced beside the central hub, is supported by a transversal bracket that protrudes from the central hub on the opposite side with respect to the hinge, and is connected to the wheels of the horizontal axle via a transversal powertrain. each pivoting wheel assembly comprising: a slewing bearing which is fixed to the chassis with the capability of rotating about said reference axis; a servo-motor which is adapted to rotate, on command, the slewing bearing about said reference axis; a horizontal axle which is located beneath the slewing bearing, is connected to the slewing bearing so as to rotate together with the latter, and is provided with at least two ground-resting wheels coaxial to one another; and an active suspension which is interposed between the horizontal axle and the slewing bearing, and is capable of varying, on command, the distance (d) between the plane on which the slewing bearing lies and rotates and the rotation axis of the two wheels; the horizontal axle of at least one of said pivoting wheel assemblies comprising: a central hub which extends between the two wheels of the axle coaxial to the wheel rotation axis and is laterally connected to the slewing bearing via a hinge that allows the central hub to swing about a first axis which is perpendicular to said reference axis and is parallel and spaced from the wheel rotation axis; and an engine adapted to drive into rotation the wheels of the axle about the common rotation axis; wherein the engine is located outside of the central hub, is arranged parallel to the wheel rotation axis, is spaced beside the central hub, is supported by a transversal bracket that protrudes from the central hub on the opposite side with respect to the hinge, and is connected to the wheels of the horizontal axle via a transversal powertrain.