I think you may have got a bit of a garbled tale about this risk. The risk isn't a general risk, it is a risk to certain people who have known conditions.
There are two main reasons to avoid viagara. The first is if you already have very low blood pressure as taking it may lower it further, by up to 8 points. It can cause you to faint. Most people don't have such low blood pressure. The second problem is if you are taking medications which include nitrates which are often prescibed for patients with certain types of coronary heart disease. It can cause very low blood pressure with certain nitrate based medications. Again, most people will not fall into this category. Most of us here probably have high blood pressure. If you ask your GP, he will know if you are at risk.
"Sex is like life, interesting in parts, but no substitute for the real thing."