“…It is effective in three ways: 1) by more complete extraction of oxygen from the blood, 2) by venous engorgement, which reduces oxygen differentials when an artery is occluded, and 3) by the production of intercoronary channels. Zoll, Wessler and Schlesinger have studied intercoronary channels in 1,050 human hearts (7). They reported the presence of anastomoses in cor pulmonale, cardiac hypertrophy and valvular lesions, and in normal hearts from patients with anemia, and suggested that in all these conditions cardiac anoxia is the underlying stimulus for development.…”