I know a fella who takes viagra and barely keeps the first woody...I know another man who can go 3 times on the same med...this is why I think ymmv

it depends on your age, what is your age and how long do you erect during the first round?

it makes it easier to get and maintain an erection.

The exception would be if a side effect of the drug is enough decreased sensitivity that one can 'lose interest'.

It will help you get hard and maintain an erection.  It will not necessarily help with a second pop in that it does nothing to increase ejaculate or encourage ejaculation, In fact, sometimes it will make your dick a bit numb making more difficult to cum.  Everyone is different. Don't use any more than you need. In the case of Viagra less is definitely more.

I use V since a spinal cord disease.  I use the smallest dose that works for one pop.  There is a study that shows delayed organsm in men with premature ejaculation.  After one pop, the erectation fades naturally, maybe slightly slower than it did before.  I've always been one pop & have learned to enjoy the journey.  I have had a few determined friends who could get me back up (mostly) & we had a second romp but there just wasn't the sensation for a second conclusion in an hour.  In all fairness, since my condition became apparent things have felt different...  fun, but different.  
jtp

Viagra improves blood flow, nothing more. The ability to bounce back and go a second round is dependent on refractory period. Some men have a very short refractory period, others are much longer. Viagra will do nothing to shorten the time it takes to recharge and be ready to go a second round.

Viagra will definitely help with maintaining a erection for a second pop.   You should be aware however, that with the ability to maintain a second erection, often comes difficulty ejaculating.  It is important to remember that the prescribed dose is a fraction of the most commonly prescribed dose on the market 100mg.  At the least this pill should be quartered to start.  Of course only your doctor can give you the best advice which may even a different med all together.
Doc

The reason that 100 mg is the most often prescribed dose of V is because there is almost no price differential between 25, 50, 100 mg doseages.  My prescribing doctor instructed me to invest in a pill cutter.  "More bang for the buck!"  (pun intended)  
The stuff tastes nasty, which is the only reason for the coating.  I swish it with a big gulp of water, problem solved.  
I've tried all the doses & frankly I have found more is NOT better.  I'm taking less than the 25 mg but it does make a difference.  
jtp

Gives me blurry vision

So ladies, if I ever blindly bump into you when you are standing right in front of me, you are in trouble.

Basically a one shot deal...........

It helps increase blood flow to the penis, so you are able to have a firmer erection, that will last throughout the first round.  It works by inhibiting an enzyme system (PDE5), and after its done its job, it's basically used up (you can only get so many miles on a tank of gas)
Basically...it let's you fuck....Not make you superman!

Re: viagra effect

I have experienced different results in different situations.  I will still feal the efects of V the next morning most of the time. The results still are all in the mind if there is not mental stimulation there are no results.  With proper mental stilulation I can go a second round almost with out a break but if there is not something pretty exciting in front of me once is it.  Dont make the mistake of taking a whole pill my doc didn't tell me about cutting pills, I learned that on my own after a severe headache and nausia and chest pain. 1/5 of a pill is enough for me.