Levitra 5 mg prevents an enzyme called phosphodiesterase-5 (PDE-5) from destroying cGMP so that cGMP persists longer. The longer cGMP persists, the more prolonged the engorgement of the penis. Levitra reduces the effect of ritonavir and indinavir. Levitra increases heart rate and also exaggerates the blood pressure-lowering effects of nitrates. In patients with chest pain (angina), Levitra can cause chest pain by increasing heart rate and lowering blood pressure. Levitra also exaggerates the blood pressure-lowering effects of alpha-blockers. Levitra also adds to the blood pressure-reducing effect of other medications.