I'm getting alerts for 80%+ CPU and memory usage on my VPS. Knownhost says it appears to be due to Heartbeat and the logs they're sending seem to indicate it's Heartbeat working in behalf of Domain Mapping. This apparently shows over 130,000 requests:
egrep 'omainmapping_heartbeat_chec' access_log|grep -c "22/Mar/2016" 130622
I haven't made any changes to my site other than general plugin updates, but this is a new problem within the last day or two.