Needs in scintimammography applications, especially for small animal cardiac imaging, lead to develop a small field of view, high spatial resolution gamma camera with a pinhole collimator. However the ideal pinhole collimator must keep a compromise between spatial resolution and sensitivity. In order to design a pinhole collimator with an optimized sensitivity and spatial resolution, the spatial resolution and the geometric sensitivity response as a function of the source to collimator distance has been obtained by means of Monte-Carlo simulation for a small field of view gamma camera with a pinhole collimator of various-hole diameters. The results show that the camera with pinhole of 1 mm, 1.5 mm and 2 mm diameter has respectively spatial resolution of 1.5 mm, 2.25 mm and 3 mm and geometric sensitivity of 0.016%, 0.022% and 0.036%, while the source to collimator distance is 3 cm. We chose the pinhole collimator with hole diameter size of 1.2 mm for our the gamma camera designed based on the trade-off between sensitivity and resolution.