PDE9A (phosphodiesterase 9A) is a highly specific cGMP-hydrolyzing enzyme that regulates intracellular cyclic nucleotide signaling. The protein exhibits exceptional selectivity for cGMP with a Km of 170 nM, making it one of the highest affinity PDEs known, while showing minimal activity toward cAMP (Km = 230 μM) 1. PDE9A functions through degradation of cGMP, thereby suppressing the cardioprotective cGMP-PKG signaling pathway 2. In cardiac tissue, PDE9A upregulation contributes to pathological remodeling by impairing calcium handling, promoting fibrosis and hypertrophy, and causing contractile dysfunction through diminished SERCA2a function and RyR2 instability 2. The enzyme is regulated by the E3 ubiquitin ligase CHIP, which facilitates PDE9A polyubiquitination and autophagic degradation 3. Clinically, PDE9A shows promise as a therapeutic target across multiple conditions. In metabolic disorders, PDE9A inhibition reduces obesity and cardiometabolic syndrome by stimulating mitochondrial activity and lipolysis in a PPARα-dependent manner 4. In cancer, PDE9A expression is downregulated in colorectal cancer tissues, with higher expression levels correlating with improved patient survival 5. Additionally, genetic studies suggest causal relationships between PDE9A and psychiatric disorders 6.