Abstract. For applications of real-time MRI, it is important but difficult to efficiently prescribe the next scan plane and obtain visual feedback on the prescription. This work addresses these issues with a 6-degreeof-freedom Plane Navigator. The Plane Navigator is a mechanical arm with integrated input and output functionality while being statically balanced. In the input mode, by holding and moving the surface normal of the physical representation of the scan plane, the operator can intuitively place the scan plane at a position with any orientation within a few milliseconds. In the output mode, the Plane Navigator automatically places the physical representation of the scan plane to reflect its position and orientation (pose)[PR1] relative to a patient domain with a maximum delay of half a second. Application examples in MRI cardiac imaging are also described.