Subject review Impossible evaluation and inadequate comparisons of heat cycles, as well as elements related to transforming ability into different energy forms by thermal efficiency degree, lead to definition of the general analytic method for evaluation of heat transfer/exchange by means of thermodynamic validity degree, due to determination of heat cycle conduct perfection level performed by conveyed and preserved exergy-available energy. On this way a correct evaluation criterion of heat transfer irreversibility present in the heat exchanger has been established.