Zaprinast is primarily known for its application as a phosphodiesterase (PDE) inhibitor, specifically targeting PDE5. This action makes it useful in research settings for studying the role of cyclic guanosine monophosphate (cGMP) in various physiological processes. It has been explored in the context of pulmonary hypertension, where it helps relax vascular smooth muscle by increasing cGMP levels, thereby improving blood flow. Additionally, Zaprinast has been investigated for its potential effects on smooth muscle relaxation in the gastrointestinal tract and its role in modulating neurotransmission. Its ability to inhibit PDE5 also makes it a compound of interest in studies related to erectile dysfunction, although it is not widely used clinically for this purpose. Overall, Zaprinast serves as a valuable tool in biomedical research for understanding cGMP-mediated pathways and their therapeutic implications.