Heart failure is a frequent often in the practice of a cardiologist but data on its actual incidence are inconsistent. This can be explained by variations in methodological approaches. Screening studies require simple easily obtainable and safe techniques capable to characterize activity of a patient. Their results should be compatible with widely accepted NYHA classification. Six minute walking test is one of possible solutions. Its results agree with NYHA classes, peak oxygen consumption and prognosis of survival. For improvement of accuracy of estimation of physical working capacity it is important to consider body mass. This can be achieved by a simple portable device constructed by the authors. To assess sufficiency of circulation during testing it is advisable to determine the load at which decorreleation between dynamics of effort and that of physiological parameters is revealed. Basing on the above considerations the authors suggest to define heart failure as a condition when decorrelation of physiological functions causes deterioration of perfusion and worsening of quality of life.