Viagra is a vasodilator. It was being developed as a antihypertensive when pfizer discovered that it had the strange side effect of causing unwanted erections. So people taking other blood pressure meds should be very careful when taking Viagra, Cialis, or Levitra. Also people with any kind of coronary artery or other cardiac diseas should be cautious also, because it can cause a drop in blood pressure. But a healthy young person who takes recommended doses of Viagra should have no deleterious effects.
BTW the stuffy nose is a unwanted effect of the vasodilation which in turn causes the desired effect. It can be cured by a run on the slopes.
End of Pharmacology Lesson.
Eddy