I have had lithos as close as 3 weeks apart. Have also had muliple lithos over the past 10 years as with my great genetics I keep creating more stones.
Unfortunately no clear information that I know of mentions how close the procedures can be done together.
I would suggest contacting both the urologist and your heart doctor and voice your concerns and see if you can get more information.
Drink plenty of water and home made lemonade is also suppose to be good also. I'd say drink beer as it makes you goto the bathroom alot but I doubt a doctor would suggest this
Good luck!