Pathological processes and aging of the organism decrease possibility of myocardium to maximal load and change it's contractility indices. Using preparations of isolated myocardial bands, we registrated atrial and ventricular isotonic contraction indices: L -length of preparation band in time of isotonic contraction, shortering speed of the band LP/dt and loosing speed dL/dt. The experiments had been performed with young, middle , old rabbits and with middle age rabbits one month after third anaphylactic shock. Maximal contraction was caused after increasing CaCl₂ (0.4 M) and addition of adrenaline into Ringer solution.

For establishing of myocardial contractility possibilities is better to express it by index contractility reserve (RR) it is possibility to increase strength of contraction, expressing absolute force. On the basis of RR index have been establisched, that young rabbits have large contractility reserve RR, while old and after third anaphylactic shock - small RR .

Comparison of contrractility reserve indices of the middle, young, old and after third anaphylactic shock rabbits revealed indices decreasing and approaching to old rabbits. So, finally it seems as if anaphylactic shock is ,,aging" myocardium.