Pimobendan (hydrochloride) (UD-CG115 (hydrochloride)) is a selective inhibitor of PDE3 with IC50 of 0.32 μM. Pimobendan (UD-CG115) exhibits selective inhibition of PDE III isolated from guinea pig cardiac muscle with IC50 of 0.32 uM compared to the inhibition of PDE I and PDE II (IC50 >30 μM). In human atrial cells, 100 μM Pimobendan (UD-CG115) significantly increases the L-type calcium current (ICa(L)) (evoked by depolarization to +10 mV from a holding potential of -40 mV) by 250.4% with the half-maximal stimulation (EC50 ) of 1.13 μM. In rabbit atrial cells, Pimobendan (UD-CG115) increases ICa(L) at +10 mV by 67.4.%, which is significantly lower than that obtained in human atrial cells. Pimobendan (UD-CG115) shows a beneficial effect on survival in the murine model of EMC virus-induced myocarditis. Administration of Pimobendan (UD-CG115) significantly increases the final survival rate from 33.6% (control) to 53.3% (0.1 mg/kg) or 66.7% (1 mg/kg). Pimobendan (UD-CG115) (1 mg/kg) also significantly reduces myocardial cellular infiltration, the level of intracardiac tumor necrosis factor (TNF)-α and interleukin (IL)-1β compared with the control group, which shows no effect on myocardial necrosis, heart weight and body weight. Pimobendan (UD-CG115) suppresses expression of the intracardiac iNOS gene , causing reduction of intracardiac NO production.