In this paper, natural convection in an inclined heated cavity with two inner cold circular/elliptical cylinders filled with viscoplastic fluids has been simulated by Lattice Boltzmann Method (LBM). In this study, the Bingham model without any regularization has been studied and moreover viscous dissipation effect has been analysed. Fluid flow, heat transfer, and yielded/unyielded parts have been conducted for certain pertinent parameters of Rayleigh number (Ra =10(4), 10(6) and 10(6)), Eckert number, the size of the inner cylinder, various inclined angles of the cavity (theta = 0 degrees, 40 degrees, 80 degrees, 120 degrees), the ratio of the inner cylinder radii (A = 0.25, 0.5, 1, 2, and 4), and different positions of the inner cylinder. Moreover, the Bingham number (Bn) is studied in a wide range of different studied parameters. Results indicate that the enhancement of the Rayleigh number augments the heat transfer, with a decrease in the size of the unyielded zones. For specific Rayleigh number and the position of the cylinder, the increase in the Bingham number declines the heat transfer and expands the unyielded sections between the inner cylinders and the enclosure. The rise of the cylinder size in the enclosure enhance heat transfer and alters the unyielded parts. The enhancement of the ratio of the inner cylinder radii augments the heat transfer and declines the unyielded sections. The increases in the vertical distance between two centers of the cylinders enhances heat transfer and moreover, alters the size and shape of the unyielded zones. The increase in the inclined angle of the enclosure alters the heat transfer and the yielded/unyielded zones noticeably. The rise of Eckert number even for higher range of practical values (Ec = 0.01, 0.1, and 1) alters the heat transfer and unyielded parts marginally, so the viscous dissipation term can be negligible in this study. (C) 2018 Elsevier Ltd. All rights reserved.