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Rotating multi-segment slant-hole (RMSSH) collimators provide much higher detection efficiency and allow fully 3D cardiac SPECT using a much lower number of camera positions as compared to conventional low-energy high-resolution parallel-hole collimators. In this study, the effects of number and placement of camera positions in RMSSH SPECT for cardiac imaging were studied, to achieve the best possible reconstruction image quality with minimal image artifacts. Both simulation and phantom experiments were performed. A modified SIMIND Monte-Carlo code and the realistic 3D NURBS-based Cardiac-Torso (NCAT) phantom were used in simulation studies. A GE 400AC/T camera equipped with a 4-segment slant-hole collimator with a 32.5° slant-angle and a Data Spectrum anthropomorphic torso phantom with cardiac insert were used in phantom experiments. Ectomography (single camera position) and RMSSH (two to three camera positions) projection data of the heart were simulated and acquired from different camera positions, and then reconstructed using an iterative OS-EM algorithm for comparison. For incomplete angle RMSSH SPECT of the heart, Ectomography gives noticeable image artifacts and distortions at any camera position. RMSSH SPECT images obtained using two camera positions 90° apart show significant improvements as compared with only one camera position used in Ectomography, and those placed symmetrically with respect to the long axis of the heart give the best image quality. For complete angle RMSSH SPECT acquisition of the heart using three camera positions, all combinations of camera positions that satisfy Orlov's condition show similar images that are of higher quality and quantitative accuracy than that from incomplete angle acquisitions. We conclude that the number and placement of camera positions in cardiac RMSSH SPECT should be chosen carefully for best reconstructed image and quantitative accuracy.