The performance of Pressure Transient Analysis (PTA) in heavy oil and low transmissivity formations is different from the conventional reservoirs, so the main objective of this work is to describe the pressure transient behavior in these low mobility-low transmissivity systems considering their impact on the main issues involved in, such as fluid viscosity, flow capacity, total compressibility and petrophysical properties. In this analysis, we present various well tests from many low transmissivity oilfields and some other heavy oil reservoirs in Mexico that produce from distinct depositional environments in sandstones and carbonates at different depths, onshore and offshore, with the objective of comparing and analyzing the pressure transient response with respect to time and the designing and execution of well tests in these types of systems. The main aspects related to the pressure transient behavior in low-mobility and low-transmissivity formations were analyzed, especially for the time required to reach the Infinite Acting Radial Flow regime (IARF) and subsequently, the pseudo-steady or steady state, where some properties are of paramount importance such as fluid viscosity, porosity, permeability, total compressibility, capillary pressure and net pay. The evaluation of the critical factors that rule the pressure transient behavior in low-transmissivity formations and heavy oils allows to identify certain patterns in transmissivity variations, determination of mean reservoir pressure, identification of reservoir heterogeneities and the corresponding influence of net pay on carbonates mainly. Furthermore, we suggest a series of recommendations about how to deal with this type of reservoirs when designing, executing and analyzing well tests for a better reservoir characterization through Pressure Transient Analysis (PTA).