Myocardial ischemia is known to provoke an excess in circulating norepinephrine and thus be related to an increased irritability of the heart. In the present experiments, we studied the norepinephrine and potassium content, oxygen tension, and pH values of the effluent of coronary sinus after thoracotomy and catheter placement into the coronary sinus. Once a steady state was reached, the measurements were repeated in the fifth, tenth, 20th, and 60th minutes of experimental myocardial ischemia provoked by coronary ligation of the left anterior descending coronary artery. The parameters obtained were compared to the corresponding values measured in the peripheral vessels. The results indicate an increased release and probably an increased turnover of norepinephrine in the ischemic myocardium. The role of metabolism acidosis in the changes in norepinephrine metabolism was suggested. It is assumed that intracellular acidosis is involved in the enhanced accumulation and release of norepinephrine in the damaged myocardium and that an increase of norepinephrine concentration in the myocardium may be considered a risk factor in supporting heart function.