Men taking nitrates such as Deponit, Nitro­Bid IV, Nitro­Bid ointment, and Sorbitrate chewable, oral, and sublingual, should not take Viagra as nitrates also tend to open up blood vessels, and when taken in combination with Viagra, blood pressure can drop to dangerous levels.  Men with poor cardiovascular conditioning and low blood pressure are cautioned in taking Viagra, as sudden, increased sexual activity can lead to overexertion, and cardiac seizures.  Viagra may cause irregular heart rhythms or arrhythmias in men who suffer from heart complications, and may reduce men's fertility.  Also, Viagra may increase the risk of Priapism, a rare but serious condition in which erections can last for more than six hours and cause significant damage to penile tissue, as well as irritation and embarrassment.

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