Turnover of heart polynucleotides, adenine nucleotides and adenosine was studied in dynamics of dog experimental myocardial infarction. In the areas of necrosis an inhibition of RNAase and DNAase was observed and later on - an activation of these enzymes with simultaneous increase in content of RNA and DNA; the stable decrease in ATP and ADP content was also found but content of AMP remained at the initial level. Conversion of AMP into adenosine was limited due to inhibition of 5-nucleotidase, whereas the direct AMP deamination and degradation of adenosine proceeded with the normal rate. Out of the necrosis area 5-nucleotidase maintained the high activity but both "non-adenosine" pathway of AMP degradation and adenosine splitting were inhibited; this promoted the nucleoside formation and maintained its level in the tissue. Alterations in content of RNA, DNA and adenine mononucleotides out of the infarction area were similar to the alterations in the impaired zone but less distinct and stable.