Grievous Wounds Question

Sorry of this is a dumb question but looking to understand grievous wounds (GW) from Morello and Executioner. I understand that people use these items against healing champs. My question is, are healing champs UNABLE to heal while the GW is active and does GW keep resetting with attacks? I am transitioning to mid lane and champs like Vlad or Akali have so much sustain. Normally I top lane and just get Executioner for champs like Fiora, but AD stats (executioner) on AP mage seems like a bad idea. Do people still buy it since Morello requires health below 35% or what do people do to counter these champs? Any and all advise would be awesome. Thank you in advance.