| My vet recommends staying on year round. If you do go off it during the winter months, most vets require you to have a heartworm test before starting again.
Think of that test as your own little insurance policy for Becky. If your pet was tested negative, is on preventative, and develops heartworm while taking the preventative, the manufacturer very often covers treatment costs.
For smaller sized dogs especially, it's often cost effective to stay on it year round rather than retest every spring. Also, most heartworm preventatives also work against several intestinal parasites, so it's not just skeeters you're protected from. | 
