I have always used Interceptor all my life on any babies that I have ever owned. However, if I don't give my kiddos their Heartworm Preventative this month (which I DO plan to - hubby is going to go and pick it up for me this week), it will be the 3rd month that they've gone without it
Can I just ask though - what is "BAD" about giving a heartworm preventative? 
I'm honestly clueless...
Also, to those who only give a heartworm preventative during the warmer months, how do you do this? I mean, once you start giving the heartworm preventative to them and then you stop for so long (for so many months), don't you have to have them tested for Heartworms to be sure that they don't have them before you start them back on the preventative again? I have always heard that this was necessary after they had been off the preventative as if they WERE to have Heartworms when you started them back on the preventative, it could kill them.