Based on a dispersion model, an extensive analysis is presented for counterflow plate heat exchangers, which takes the deviation from ideal plug flow into consideration to predict the response due to temperature transients. The analysis also incorporates solid longitudinal conduction and solid as well as fluid heat capacities, and simulates the exit temperatures of both fluids for any given arbitrary temperature transient at the inlet(s). It is found that the ’phase lag effect’, which is a special characteristic of plate exchangers, plays a significant role in the dynamic regime. The examples are presented for step and sinusoidal response and the effect of U- and Z-type configurations has been discussed. The method is based on the Laplace transform and it utilizes numerical inversion of the Laplace transform. The results lead to the conclusion that the effect of flow maldistribution and ’phase lag’ plays an important role, particularly when the decreasing flow velocity in the gasket ports is taken into consideration.