Pimobendan (UD-CG 115 BS) is a selective inhibitor of PDE3 (IC50: 0.32 μM).

PDE3:0.32 μM

Compared to the control group, Pimobendan (1 mg/kg) significantly reduced the permeability of cardiomyocytes and also decreased the levels of TNF-α and IL-1β within the chamber without affecting myocardial nerves, heart weight, and body weight. In a mouse model of EMC virus-induced myocarditis, Pimobendan contributed to an extension of lifespan. The final survival rate was significantly increased from 33.6% (control group) to 53.3% (0.1 mg/kg) or 66.7% (1 mg/kg). Additionally, Pimobendan inhibited the expression of inducible nitric oxide synthase genes in the heart, thereby reducing the content of nitric oxide within the heart.

When administered to human atrial cells, Pimobendan (100 μM) increased the L-type calcium current by 250.4% (EC50: 1.13 μM). Its effect on rabbit atrial cells was significantly lower, resulting in a 67.4% increase in ICa(L). Pimobendan exhibits selective inhibitory action on isolated PDE III in guinea pig myocardium (IC50: 0.32 μM), with much higher IC50s for PDE I and PDE II (>30 μM). It also inhibits cAMP-PDE III activity (IC50: 2.4 μM) and induces a positive inotropic effect on isolated guinea pig papillary muscles (EC50: 6.0 μM), partially due to its selective inhibition of myocardial PDE III.