This study presents a two-dimensional numerical investigation of natural convective heat transfer within a square vented enclosure heated by two horizontally placed cylinders. The enclosure features a top and bottom opening, with its aspect ratio (the width of the opening relative to the enclosure's width) incrementally varying from 0.1 to 1.0. Steady, laminar, and incompressible fluid flow is modeled using the COMSOL Multiphysics computational fluid dynamics software across a Rayleigh number (Ra) spectrum of 10⁴ to 10⁶. Results indicate that at a low Ra of 10⁴, streamlines remain highly uniform, producing only minor vortices at aspect ratios of 0.1 and 0.2, which disappear entirely at full openings where the aspect ratios are 0.9 and 1.0. Conversely, elevating Ra to 10⁵ and 10⁶ intensifies vortex formation at the right top and bottom sections for aspect ratios up to 0.8, though full openings still prevent any vortex generation. Thermal analysis demonstrates that at Ra = 10⁴, the average Nusselt (Nu) number correlates positively with increased aspect ratios. At higher buoyancy levels where Ra is 10⁵ and 10⁶, the Nu number increases for aspect ratios between 0.1 and 0.5, but experiences a decrease when the opening ratio ranges from 0.6 to 1.0. Ultimately, this research offers a comprehensive theoretical framework detailing how opening size and Rayleigh numbers interact to influence flow and thermal dynamics in dual-cylinder vented configurations.