This study relates to an evaluation of the thermo-hydraulic performance for a state-of-the-art compact brazer plate heat exchanger (PHE) in 3 kW for 3-plates. To improve heat transfer and pressure drop of the PHE, a lung pattern is designed at certain heights on the plate surface by using biomimetic approach in first time. It is known that human pulmonary system is one of the most effective heat exchanger devices in the nature. Its tree like structure provides good compactness, consequently better heat transfer rate per unit volume. By means of achievements in additive manufacturing technologies in recent years, a heat exchanger with any desired plate or fin geometry can be manufactured. In this study, plate surfaces have been designed as a 3D lung like structure in order to increase the heat transfer area. CFD simulations are then performed with Ansys-Fluent program in operating condition under supply temperatures of 90 degrees C and 40 degrees C with a mass flow rate of 0.05 kg/s for hot and cold sides, respectively. The simulation is validated by the numerical and experimental results of an existing Chevron type compact brazed PHE. The results show that there is a 71.30% increase in heat transfer and a 67.8% decrease in pressure drop for 6.66% less volume compared to the reference PHE. The effectiveness of the lung patterned PHE is found to be 0.350. Fluid velocity in plate cavities on lung pattern is quite irregular due to turbulence formation at almost constant Reynolds numbers. This increases its effectiveness. Finally, lung patterned plates designed with biomimetric method is a guideline study to improve the performance of PHEs.