Internal mammary artery (IMA) flow patterns were analyzed in a dog model without interference with the coronary artery bed (n = 6, mean bodyweight: 21 +/- 4 kg) during the following conditions: a) baseline values and steady state: b) acute hypovolemia (withdrawal of 20% of circulating volume over 90 s): c) retransfusion (same volume over 90 s): d) progressive hypovolemia (withdrawal of the same volume over 240 s): e) bolus of nitrates (500 micrograms/kg over 60 s).