I would have to agree with what most people have been saying. If you have 2 competent heals try two healing, if not 3 healing is fine, 4 healing should not be considered. The goal should be to push each head before 3 breaths on the tank. CD's need to be coordinated including non healer cds.
For instance, as a shaman if you go back to your dps spec when the healing gets sketch you can drop your tide and that will be as adequate a healing cd as you spamming chain heal/ healing circle shit.
Remember with shorter healing cds you can get away with using them twice if it is timed correctly (this should be done say 2nd and 5th head or 3rd and 6th head) to minimize healing.
Lastly, avoid all avoidable damage dispell quickly (make sure melee are moving out quick) and get away from the green shit asap.
GRGRGRG Good Game