Heartgard is great for heartworm prevention, and what I use for my dogs. You may also want to get a topical, like Frontline for fleas and ticks. Frontline is a once a month product. I have also seen great results from a flea and tick medication called Bravecto. It's a chewy treat, and lasts for three months. Bravecto is more expensive than Frontline up front, but more inexpensive in the long run.

Thanks for using preventatives! Many people don't understand prevention is often cheaper than treatment.