Authors measured the concentration of stable metabolite (NO2: nitrite) of EDNO (endothelium derived nitric oxide) in the internal mammary artery (IMA) bypass graft with the help of a previously reported method (measurement of effective blood flow capacity of the IMA graft in the coronary sinus). Nitrite level in the systemic circulation prior to extracorporeal circulation (ECC)--(68.1 +/- 6.7 mumol/l) was measured, as well as nitrite concentration in the coronary circulation before and after construction of the IMA bypass graft (62.1 +/- 4.19 mumol/l and 50.26 +/- 4.0 mumol/l respectively). Furthermore, nitrite level in the IMA graft free cut end flow was also determined (64.3 +/- 5.9 mumol/l). These data compared to the nitrite levels in the normal plasma (48.1 +/- 5.9 mumol/l) were found to be higher (p = 0.1, ns.), possibly due to the enhanced EDNO production induced by total heparinization. The nitrite concentration in the IMA free cut end flow is similar or slightly higher than that of the native coronary circulation, however, after IMA bypass construction a relative reduction could be measured in the coronary sinus. Authors believe, that this may be related to the reduction of basal EDNO production caused by supernormal pO2 (215 +/- 19 mmHg) during ECC.