An imaging system for imaging a periodically moving object, the imaging system comprising: - an ultrasound signals providing unit (13, 16) for providing ultrasound signals of the object for different times, - a phase signal providing unit (17, 36, 37) for providing a phase signal being indicative of motion phases of a periodic movement of the object at the different times, - an assigning unit for assigning the ultrasound signals to the motion phases based on the provided phase signal, - an ultrasound images generation unit for generating several ultrasound images for the different motion phases, wherein an ultrasound image for a motion phase is generated based on the ultrasound signals assigned to the respective motion phase, and - a display control unit for controlling a display unit, wherein the display control unit is adapted such that the generated ultrasound images are temporally consecutively displayed on the display unit for showing the periodic movement of the object, characterised in that the ultrasound signals providing unit (13, 16) is adapted to temporally consecutively provide A-lines as the ultrasound signals, wherein the ultrasound images generation unit is adapted to generate M-mode images as the ultrasound images and to update the M-mode images generated for the different motion phases by appending actually provided A-lines, which have been assigned to the respective motion phases, to the respective M-mode images and wherein the display control unit is adapted to control the display unit to display the updated M-mode images temporally consecutively for showing an updated periodic movement of the object. - an ultrasound signals providing unit (13, 16) for providing ultrasound signals of the object for different times, - a phase signal providing unit (17, 36, 37) for providing a phase signal being indicative of motion phases of a periodic movement of the object at the different times, - an assigning unit for assigning the ultrasound signals to the motion phases based on the provided phase signal, - an ultrasound images generation unit for generating several ultrasound images for the different motion phases, wherein an ultrasound image for a motion phase is generated based on the ultrasound signals assigned to the respective motion phase, and - a display control unit for controlling a display unit, wherein the display control unit is adapted such that the generated ultrasound images are temporally consecutively displayed on the display unit for showing the periodic movement of the object, characterised in that the ultrasound signals providing unit (13, 16) is adapted to temporally consecutively provide A-lines as the ultrasound signals, wherein the ultrasound images generation unit is adapted to generate M-mode images as the ultrasound images and to update the M-mode images generated for the different motion phases by appending actually provided A-lines, which have been assigned to the respective motion phases, to the respective M-mode images and wherein the display control unit is adapted to control the display unit to display the updated M-mode images temporally consecutively for showing an updated periodic movement of the object.