Full disclosure - I have done it many times. I won't judge you :)

What to do now: 

If it's been less than 3 months, you're still in the clear to restart prevention now and plan a heartworm test in 6 months.

If it's been over 6 months, give us a call first — a quick blood test can help keep your pup safe.

I just created these two slides to explain heartworm in dogs a bit more. It's a nasty disease, but it takes quite some time to develop, so you don't need to panic.