<prompt> Use of tadalafil is contraindicated in:Pulmonary arterial hypertensionUnstableSymptomatic anginaActive infectionsHepatic dysfunction  <response>: Ans. b. UnstableSymptomatic anginaRef: Goodman Gilman 12th eP. 841Nitrates increase cyclic GMP production by stimulation of guanylate cyclase via NO. This cyclic GMP is responsible for vasodilation.Cyclic GMP is metabolized by PDE-5 and hence PDE-5 inhibitors like sildenafil and tadalafil can significantly increase cyclic GMP producing fatal hypotension.Thus tadalafil is contraindicated with nitrates and hence unstablesymptomatic angina is the best answer. 