Calculation of free convection heat transfer from isothermal bodies of different shapes is of fundamental importance in science and engineering. In the present study, a new analytical model is developed to calculate laminar natural convection heat transfer from finite isothermal cylinders of arbitrary aspect ratio and orientation (vertical, horizontal, and inclined) with active ends in fluids of any Prandtl number. This method is based on the new concept of Dynamic Body Gravity Function. Also, a new dimensionless parameter called Body Fluid Function is introduced and applied in this method. Results of this dynamic model are presented for six different circular cylinders and compared with the available experimental data. Excellent agreement is found between the developed model and experimental results in a wide range of Rayleigh number for all cylinders discussed. This shows that the present method is a powerful tool for modeling laminar natural convection from isothermal bodies.