A system, comprising: a windowing component that is adapted to receive an ECG signal that includes a premature heart cycle, which is one that occurs earlier than expected, wherein the ECG signal is time-synchronized with x-ray projection data of a beating heart and wherein the windowing component is adapted to position a first reconstruction window within a first heart cycle to correspond to a desired cardiac phase, said reconstruction window defining a plurality of reconstruction windows (504, 508, 512, 516) each located in a different cardiac cycle (304,308,312,316); characterised by an analyzing component that is adapted to recognize that a reconstruction window (412, 512) does not correspond to the desired cardiac phase and to determine whether a data gap occurs if said reconstruction window is removed by determining whether the data corresponding to the remaining reconstruction windows provides sufficient data for reconstruction purposes such that there is no missing data; a recommendation component; and a reconstructor that is adapted to reconstruct projection data corresponding to a plurality of reconstruction windows from different cardiac cycles and to generate image data indicative of the desired phase of the heart, wherein the windowing component is adapted such that the reconstruction window is removed if there is sufficient data and remaining reconstruction windows or data corresponding thereto are selected for reconstruction by the reconstructor and adapted such that in case of insufficient data the recommendation component provides a global recommendation of a different phase or different phases located before the premature heart cycle and wherein an effected reconstruction window is movable, reconstruction windows or data corresponding thereto are selected for reconstruction by the reconstructor and wherein the analyzing component in that case determines whether a data gap has been introduced by moving of the reconstruction window. a windowing component that is adapted to receive an ECG signal that includes a premature heart cycle, which is one that occurs earlier than expected, wherein the ECG signal is time-synchronized with x-ray projection data of a beating heart and wherein the windowing component is adapted to position a first reconstruction window within a first heart cycle to correspond to a desired cardiac phase, said reconstruction window defining a plurality of reconstruction windows (504, 508, 512, 516) each located in a different cardiac cycle (304,308,312,316); characterised by an analyzing component that is adapted to recognize that a reconstruction window (412, 512) does not correspond to the desired cardiac phase and to determine whether a data gap occurs if said reconstruction window is removed by determining whether the data corresponding to the remaining reconstruction windows provides sufficient data for reconstruction purposes such that there is no missing data; a recommendation component; and a reconstructor that is adapted to reconstruct projection data corresponding to a plurality of reconstruction windows from different cardiac cycles and to generate image data indicative of the desired phase of the heart, wherein the windowing component is adapted such that the reconstruction window is removed if there is sufficient data and remaining reconstruction windows or data corresponding thereto are selected for reconstruction by the reconstructor and adapted such that in case of insufficient data the recommendation component provides a global recommendation of a different phase or different phases located before the premature heart cycle and wherein an effected reconstruction window is movable, reconstruction windows or data corresponding thereto are selected for reconstruction by the reconstructor and wherein the analyzing component in that case determines whether a data gap has been introduced by moving of the reconstruction window.