HEARTGARD Chewables is well tolerated. In the clinical studies involving more than 3,000 doses of HEARTGARD for Cats, observations reported within 24 hours of treatment included vomiting in =0.3% and diarrhea in =0.2% of the doses administered. There was no statistical difference between HEARTGARD Chewables for Cats and the product vehicle (control) for these observations. For more information, contact your veterinarian or visit www.HEARTGARD.com. Click here for Product Information - Cat.