An isothermal reaction-diffusion system is considered in a two-dimensional fluid medium within a gravitational field. Inhomogeneities in the concentration field of the species give rise to a fluid flow due to buoyancy forces. A two-dimensional reaction-diffusion-convection model of an excitable medium is presented. The influence of hydrodynamics on spiral wave dynamics is systematically studied. A kinematic model is also introduced to better understand the mechanisms involved here.