Fig. 1. Scheme of the perfusion set-up. The isolated heart was mounted into a saline-filled, temperature-controlled chamber. The coronary cannula was connected to two input reservoirs, one filled with saline (maintained at constant level by a re-circulating pump; not shown) and the other filled with the red blood cell (RBC) suspension. Perfusion could be shifted between the two reservoirs via a three-way tap. Each reservoir was associated with a coronary flow measurement device similar to that described by Agnisola et al. (1994), but computer controlled. The aortic cannula was occluded so the output from the preparation was into the chamber via the atrial cannula. An ISO-NOP electrode was inserted into the atrial cannula to measure relative changes in NO level in the effluent from the preparation. The saline level in the chamber was kept constant by an overflow. Samples could be taken from both input and atrium.