A computed tomography system (100) includes a windowing component (140) that receives an ECG signal that includes a premature heart cycle. The ECG signal is time-synchronized with x-ray projection data of a beating heart. The windowing component (140) either removes or repositions a first reconstruction window within a first heart cycle to correspond to a desired cardiac phase when the premature heart cycle causes the first reconstruction window to correspond to a different cardiac phase, based on available data. A reconstructor (148) that reconstructs projection data corresponding to a plurality of reconstruction windows from different cardiac cycles generates image data indicative of the desired phase of the heart.