Inotropic, Vasodilator and Low Km, cAMP‐Selective, cGMP‐Inhibited Phosphodiesterase (PDE III) Inhibitory Activities of 4a‐Methyl‐4,4a‐ dihydro‐5H‐indeno(1,2‐c)pyridazin‐3(2H)‐ones and 4a‐Methyl‐4,4a,5,6‐ tetrahydrobenzo(h)cinnolin‐3(2H)‐ones.