We have investigated the time profiles of flare heating function for selected flares based on the analysis of their evolutionary paths in the Emission Measure - Temperature diagrams. The emission measures and the temperatures werederived from the Ca XIX soft X-ray spectra observed by the Bent Crystal Spectrometer aboard the Solar Maximum Mission satellite. Interpretation of these diagrams allows to study the rate of energy deposition during both rise and decay phase of flares. The investigation of (EM-T) diagrams during
the decay phase allows furthermore for determination of effective length/cross-sectional area ratio of the flaring loop. We háve used the value of this ratio to derive the effective loop cross-sectional radius and the plasma density from deconvolved Fiat Crystal Spectrometer soft X-ray images.