K134 (K-134) significantly prolongs middle cerebral artery (MCA) occlusion time at doses >10 mg/kg, and reduces cerebral infarct size at 30 mg/kg in the stroke model (n?=?12, 87.5±5.6 vs. 126.8±7.5 mm³, P<0.01), indicating its potent antithrombotic effect. The overall bleeding risk of K134 is assessed in general in mice. Single oral administration of K134 does not prolong bleeding time at a dose of 30 mg/kg compared to control (106±5 vs. 110±5 s, not significant). Moreover, a sufficiently high enough plasma concentration of K134 (13.6±2.3 μM) is detected to inhibit platelet aggregation at 10 min after single administration in mice at a dose of 30 mg/kg, which is the same time point as the above test of bleeding time. Next, the effects of PDE3 inhibitors on thrombus formation are also investigated in an arteriovenous shunt model in rats. K134 significantly reduces the incidence of occlusive shunt thrombi at doses above 10 mg/kg (half-maximal effective dose: ED₅₀=11 mg/kg). The plasma concentration of K134 is 0.43±0.08 μM (C_max) at a dose of 10 mg/kg^[1].