These side effects are generally not dangerous, but consult your doctor if they persist or are particularly bothersome. Cialis helps you get and keep stronger erections with a daily or as-needed pill. Your physical health. The most common side effects of Viagra are headaches, facial flushing, dyspepsia indigestion , changes to your vision, nasal congestion, back pain, muscle pain, nausea, dizziness and rash. Make sure to inform your healthcare provider about all medications you currently use before you use Viagra. If you want around-the-clock ED treatment, daily dosages of Cialis or Tadalafil might be right for you.Viagra is an effective drug for treating male erectile dysfunction, but it targets sexual performance, not sexual arousal. There is limited evidence that Viagra may be beneficial for women with sexual dysfunction, but the . 1. How it works. Sildenafil may be used to treat erectile dysfunction (ED or impotence) in men (Viagra brand) or pulmonary arterial hypertension in both men and women (Revatio brand), depending on the brand. Sildenafil blocks the action of an enzyme known as cGMP-specific phosphodiesterase type-5 (PDE-5).  · 3 Answers. Viagra works in response to sexual stimulation to increase the blood flow to the penis leading to an erection. Viagra does not result in an erection without sexual stimulation. When a man is aroused, muscles in the penis relax to allow this greater blood flow. Viagra helps to elevate the levels of a substance (cyclic guanosine.