The presente work investigated experimentally and numerically the heat transfer and pressure drop characteristics of turbulent decaying swirl flows through a rectangular duct of high aspect ratio. The swirl flow inlet condition was obtained by a set of parallel tubes with twisted-tape inserts wich produced pairs of counterrotating vortices. Local and average heat transfer coefficients were determined by the utilization of the naphthalene sublimation technique in conjunction with the analogy between heat and mass transfer. Local result were obtained along the whole active surface of the duct, utilizing a computer-assisted coordinate table and depth gage. The study encompassed the investigation of the local and average heat transfer coefficient distribution and pressure drop, for three values of the duct Reynolds number, and for three values of the swirl intensity given by different tape pitch-to-diameter rations. The results showed regions of high heat transfer augmentation situated close to the entrance of the duct, when compared to the base case results characterized by turbulent flow through a duct without the swirl flow inlet condition. The pressure drop results demonstrated that the presence of the tangencial velocity component of the imposed swirl flow was seen to reduce the pressure recover effect present in sharp-edged entrance ducts. It was also verifyied that the hydroninamic developing length increases with the intensity of the swirl flow. The equations governing conservation of mass, linear momentum and energy were solved numerically for the configuration investigated. The K-E turbulence model was employed. The numerical results displayed good agreement with the experiments and provided additional information related to velocity and temperature fields which complemented the experimental program.