In other words, where heartworm is seasonal, there is no good reason to give year - round heartworm drugs. (littlebigcat.com)
However, the good news is the safety margin for heartworm drugs is very high. (dogs.lovetoknow.com)
That means giving your dog heartworm drugs every month, year round, to protect her... and asking your vet to test her every 12 months for heartworm disease. (dogsnaturallymagazine.com)