you just did the best possible thing a person can do to help someone in dire need, and now with the advent of cheaper semi automatic difbrilators(AEDs) in many many more public places, the odds of someone actually surviving a full cardiac arrest and tons better than even five years ago.
it comes down to early recognition of the cardiac symptoms, calling 911 as early in the event as possible, and if that patient goes down, getting on that chest with compressions asap. if there is ever an AED hanging around, integrating that one thing into the mix is what really has saved many many lives. they are very simple to use and can bring someone back from the two most common reasons for a heart attack, either V fib or V tach. those are the only rhythms the AEDs will shock.
more people should take time to do what you did. just take one or two nights out of their lives to learn how to do this properly. sorry your grandpa had to go thru this and you had to see that. i know from many years of experience in running full codes working as a ff/emt just how scarey some can be. and not knowing what to do just makes it that much scarier. but getting 911 called ASAP is the best thing to do so you just DO have everyone coming and on the way(the second someone complains of cardiac symptoms), and you can do what needs to be done if something happens. you just did a wonderful thing for others. hopefully you will never ever have to use it, but at least you do know how. good job. FB