An investigation was made of the possible release from heart muscle of substances of small molecular weight following experimental myocardial infarction. These resulting chemical changes in coronary vein blood may be due to metabolic alterations of the cell which would either precede cell death or take place in cells with reversible metabolic changes. The coronary arteriovenous differences of pyridine nucleotides, thiamine and its phosphorylated derivatives, amino acids and amino sugars were investigated. No changes from the control were found. The negative results may have been caused by the rapid turnover of these substances in blood.