PDE5A and ischemia: The cardioprotective effects of the supernatant were mimicked by administration of exogenous cGMP to the hearts at the onset of ischemia (Figure 3, A and B and Supplemental Figure 3), and this effect was, similar to that of the supernatant, abolished by PDE5 (Figure 3C) and by MK571 (Figure 3, A and B).