I found a good description of Lasix at
http://www.drugs.com/lasix.html
If you decide to use the above link you will have to copy it into your browser, is it not a hyperlink.
I did not read the complete description on Lasix, but as it reduces your retention of water, you need to take care to remain hydrated.
If you're being paced part of the time, I've never heard of breathing problems associated with that. If the ICD fires off, you'll know that. I've read of some folks having diaphragm spasms from a problem pacer which give the patient a feeling like hiccups but again, not shortness of breath.
Considering you need the ICD/pacer it must mean you have CHF and will be prone to fluid retention. A diuretic is the usually way to go. Don't forget to reduce your sodium intake, not just the salt shaker but look for sodium of any kind on the food packages. Even natural foods like celery or carrots have some sodium in them. Have you ever looked at the sodium content in packaged dinners, canned soups or condiments? Scary.