There are several options for heartworm preventatives. 1) Heartgard for small dogs, 0-25 pounds 2) Heartgard for small cats, 0-5 pounds. 3) Interceptor for small dogs, 0-10 pounds 4) Revolution for large cats, 5-15 pounds or 5) diluted ivomec. 20 to 200mcg/kg Hope that helps, Jerry Murray, DVM [Posted in FML issue 3745]