Nowadays, chaotic advection flow is one of the most useful methods to enhance mixing and heat transfer simultaneously in laminar flow that generated by spatially chaotic trajectories of the fluid particles. In the present study, numerical simulation of chaotic advection flow and heat transfer in laminar flow in a twisted pipe are performed by Ansys Fluent software. The geometry consists of three successive bends of elliptical cross-section in macro dimension which a uniform and pulsatile velocity field imposed as the inlet condition and the walls are subjected to a constant temperature and constant heat flux. The variation of secondary flow structures is investigated for demonstrating the behavior of chaotic flow in a twisted pipe. The appearance of homoclinic and heteroclinic connections and stretching and extending of elliptical orbits in the secondary flow structures and increasing the variation of secondary flow patterns in one cycle of pulsating flow are the signs of chaos in the fluid flow. The more chaos in the flow represents mixing enhancement, but since analysis of secondary flow structures is a qualitative criterion of chaos, vorticity vector method which describes stretching and engulfment of flow, is used to give a quantitative criterion of chaos. For the quantitative evaluation of heat transfer, Nusselt number and standard deviation of temperature are measured and for the qualitative evaluation of heat transfer, the temperature profiles and contours at the exit of the bends are analyzed. In addition, for investigating the efficiency of system, pressure drop is calculated for different cases. In both steady and unsteady states flow, according to secondary flow patterns, when the Reynolds number and wall temperature increase, the elliptical orbits and homoclinic connection develop and finally improve mixing and heat transfer enhancement. Moreover, in pulsating flow the higher values of velocity amplitude ratios (?) and lower and medium values of Womersley numbers (2.1118???3.9509), promote the chaos in fluid flow and provide the best condition for mixing and heat transfer. In both steady and pulsating flow, increment of Reynolds number, decreases heating homogeneity and increment of wall temperature, promotes heating homogeneity. It is also observed that increment of Womersley number in pulsating flow, decreases heating homogeneity. The results of quantitative and qualitative assessment for determining the optimum cross section between four shapes (elliptical, circular, rectangular, square) for mixing show that if the problem of pressure and energy loss are not significant and mixing enhancement is the main purpose, the elliptical cross section create the best condition for mixing. On the other hand the circular cross section has minimum pressure loss between the other cross sections and has more mixing enhancement than the square and rectangular cross sections. Therefore from the economical viewpoint, circular cross section is more favorable than the others. Keywords: Chaotic advection, Mixing, Heat transfer enhancement, Secondary flow patterns, Vorticity vector, Homogeneous heat transfer, Twisted pipe