Fig. 1. (A) Scheme of the perfusion apparatus (left) connected with the amperometric gas sensor (right) used for nitrite detection in the cardiac effluent. (B,C) The myoarchitecture of the icefish heart showing the extensive and fully trabeculate ventricular wall. (B) Histological longitudinal section (Sirius Red staining) (bar, 0.25 cm); (C) scanning electron micrograph with details of the myocardial trabeculae and the intertrabecular spaces (lacunae) (bar, 100 µm). (D) Transmission electron micrograph showing mitocondria and myofibrils in ventricular myocytes. (J. M. Icardo and B. Tota, unpublished material). P, perfusate; PT, pressure transducer.