The left ventricle myocardium and chamber segmentation in gated SPECT images is a challenging problem. Segmentation is however the first step to geometry reconstruction and quantitative measurements needed for clinical parameters extraction from the images. New algorithms for segmenting the heart left ventricle myocardium and chamber are proposed. The accuracy of the volumes measured from the geometrical models used for segmentation is evaluated using simulated images. The error on the computed ejection fraction is low enough for diagnosis assistance. Experiments on real images are shown.