The ultimate objective of the research which led to this thesis is to increase the efficacy and safety of radiofrequency catheter ablation (RFCA) of cardiac tissue. The purpose of RFCA is to carefully heat selected locations in the heart. The resulting thermal injury creates lesions which prevent the generation or propagation of arrhythmias. The ability to predict the appropriate amount of energy required at any ablation site is essential to increasing the efficacy and safety of RFCA. The research documented in this thesis focuses on the development of an approximate thermal model of the time-dependent temperature profile within the myocardium during an RFCA procedure. It is anticipated that this model will ultimately give electrophysiologists the ability to accurately titrate energy delivery in clinical situations. The approximate thermal model uses a convective boundary condition to account for convective cooling of the myocardial surface. This model also uses a point source rather than the complicated heat generation function that accounts for the spatial variation of the voltage in the cardiac tissue. A C program was written to evaluate the engineering model. The effect of the convection coefficient (h), the depth at which the point source is located (zo), and the power dissipation rate (P) on the 50 ˚C isotherm in the cardiac tissue is shown. The accuracy of the approximate model depends greatly on the values of these three parameters. Rigorous three-dimensional numerical modeling was done in order to validate the engineering model. The numerical model was done using a commercial computational fluid dynamics (CFD) package. This software solved the steady, incompressible Reynolds-Averaged Navier-Stokes (RANS) equations—along with the Reynolds-Averaged energy transport equation—using an unstructured, segregated, pressure-based finite-volume procedure. This model is different from other numerical RF ablation models in that it took into account the turbulent flow of the blood. It also accounted for the effect of the flow past the electrode and the spatially varying heat generation function. The heat generation function was found from the solution of the Laplace equation to find the voltage distribution in the tissue. The three unknown parameters governing the approximate thermal model were changed manually and good fits of the approximate model with the numerical model resulted, proving that the engineering model can accurately predict the size of the 50 ˚C isotherm in the cardiac tissue.