Heal is a skill reflecting your ability to tend wounds and ailments. It uses the Wisdom stat as a modifier
This skill focuses on dying rules and aiding people afflicted by poison/wounding.
What can you do with Heal?
This skill allows you to stabilize the dying and increase the number of hit points recovered from rest. You can also alleviate certain conditions such as movement reduction from spike stones, caltrops and spike growth.
Once per day you can use this to restore hit points to damaged creatures, 1 per hit die, + your wisdom modifier if you roll a 25 or greater. You can finally use a successful heal check to increase a poison or disease save by +4.
Which of these have ground for use?
If you are going to allow healers to improve the save chance by +20% I can see the chance of success of the skill being useful for that - but as far as giving up your combat round to bandage someone who is bleeding out it is annoying to have the possibility of failure. Is what we are doing here simulating realism? Regardless, the check for first aid is just 15, which means this is another skill where a first level character with any wisdom bonus at all with heal as a class skill can just take ten to succeed which for all intents and purposes turns this into a function of class role.
When recovering hit points during resting, do you want the player to roll every day for greater hit point gain? Does anyone play that way?
There are people who would make the argument of game design from realism - perhaps they are too badly wounded to staunch the wound. Perhaps they might not succeed at stopping the bleeding. Again, I am not concerned for realism in games, I'm concerned about having fun with my friends. I don't consider a situation where one person is already out of play waiting for the combat to be over improved by taking another person out of play for multiple turns because the rolled low.
What is it we gain by having this skill?
Primarily a method of allowing non-cleric/druid/paladin/rangers to fulfill their roll by level 5.
What do we lose?
The mini-game of 'give up your turn to keep another player from dying' win/lose dynamic can increase tension and interest, but I remain unconvinced it's actually fun. It reminds me of streaks where I miss in battle and the associated frustration, except now it sucks for the player who can't do anything while they are bleeding out as well as the person who for some reason can't stop their bleeding/poison.
I also do not see any advantage in tracking these rolls and increasing resting hit points. It is less fun then other activities that can be taking place.
Conclusions & Suggestions:
I would eliminate this skill entirely, and simply allow PC's to give up their turn to bandage their fellows when they fall in battle. I allow anyone with a character trait focused on healing or first aid to provide that aid to those that are poisoned or wounded at the cost of an turn either in combat or out- more then enough of a cost to justify the benefit.