Cardiac failure is a disease which involves three different mechanisms: (1) the limits and imperfections of the general process of myocardial adaptation to mechanical stress, which includes various changes in genetic expression, including an increased collagen mass, but an unchanged collagen concentration; (2) the limits and imperfections of the adaptational process at the peripheral level which allows the entire organism to adapt to the low cardiac output; (3) fibrosis, an augmented collagen concentration, which is not a direct consequence of mechanical overload, but depends on aging, myocardial ischemia or hormonal changes. Middle-aged spontaneously hypertensive rats (SHRs) represent a good model of the common clinical situation. Three-month treatment with a CEI reduces, in parallel, arterial hypertension, left ventricular hypertrophy and ventricular fibrosis. Holter monitoring was also performed in these animals. Untreated SHRs when compared to age-matched Wistar rats have an increased number of ventricular premature beats which are suppressed by the treatment. In addition, heart rate variability has been quantified by using the pseudo Wigner-Villé transformation, a time and frequency domain method. The low frequency oscillations are hampered in SHRs. CEI normalizes this parameter.