Hi Pacer –
There’s no alternative to Heartguard. There aren’t any natural treatments with demonstrated efficacy. I have my dogs on Heartguard (well, not Heartguard brand but an equivalent) and – imo – the basic ivermectin based preventatives are very safe. I only give it when the temperature is high enough for mosquitoes to transmit heartworm and for three months after the temperature drops (so for Northern NY that’s roughly April/May – November/December), I dose every 45 days (vs. every 30 which is recommended on the package) and give milk thistle for a week following each dose.
