I'm actually a little confused here. You said you vape, and your grandma is the one with the heart condition. I'm understanding 3 separate scenarios here, and I'm wondering which one you're asking. 1, You vape, and your grandma wants to try vaping too. 2, you're worried about your second hand vape hurting your grandma. 3, You're worried that vaping might somehow cause you to develop congestive heart failure in the future. So here are my answers by scenario:
1. If your grandmother wants to try vaping with congestive heart failure, she needs to talk to her doctor first. But it's probably not a good idea. Stimulates don't generally bode well with serious heart conditions. Is she advised to avoid caffeine? If not nicotine is probably out too. That said, if she's currently a smoker who can't quit, vaping is probably the better choice.
2. Unlike smoke, vapor settles withing minutes of being expelled from your lungs. Coupled with the very low dose you're vaping, I wouldn't think it would be much of a concern. But if you're worried, just don't vape around her.
3. No one can say whether or not you'll have heart problems in the future. But it's generally accepted in the vaping community that nicotine affects the body much like caffeine. If you end up with a heart condition in the future, it is likely that such a thing was already in the works for you, genetically.
All that said, no one knows for sure the long term effects of vaping. It could turn out that vaping plays a role in cardiovascular disease. There don't seem to have been any serious complications in the short term. Same goes with lung disease. We just don't know at this point. However, if I were you I'd absolutely hedge my bets that cigarettes are far worse.