Apparently they moved it to AWS in the past day, perhaps to recover from the outage.

During the outage heartbeat.belkin.com resolved to 67.20.176.130 which is held by Sungard.

We (and several other ISPs) got our customers back online by putting 67.20.176.130/32 on a loopback interface on one of our routers so it would always respond to pings. Other ISPs put overrides in their caching DNS servers so heartbeat.belkin.com always resolves to 127.0.0.1 (belkin.com doesn't roll DNSSEC).