Some fused 5H-pyridazino[4,5-b]indoles (7-10), substituted in positions 1 and 4 by hydrazine and/or amino groups, have been synthesized. These new compounds present a planar topography, a dipole with an adjacent acidic proton, and a basic hydrogen-acceptor site opposite the dipole. These compounds have some resemblance to carbazeram and other pyridazino agents with cardiotonic activity. Some of the new compounds here described possess inotropic activity (Table I and II), with a complementary effect as inhibitors of platelet aggregation (Table III and IV). 1-Hydrazino-4-(3,5-dimethyl)-1-pyrazolyl-5H-pyridazino[4,5-b ]indole hydrochloride (7a.HCl) is the first compound described in the literature with activities as inhibitor of PDE-IV and as selective inhibitor of TXA2 synthetase (Table V).