In patch 8.6, Heal was crowding out other options in mid lane, so we lengthened its cooldown. This pushed both marksmen and mid laners onto teleport (which has had a much more notable impact on the meta), so we're reverting the Heal nerf.
COOLDOWN :  ⇒ 240 seconds
In general, defensive spells should have higher cooldowns than offensive spells. That is, if two opposing player uses Heal and Ignite in the same fight, there should be a window where the Ignite player has a summoner spell edge and can try and make another play. Currently, Heal's cooldown is probably a bit too low for players to take advantage of that disparity, so we're upping it.
COOLDOWN :  ⇒ 270 seconds
Less heals for all.
- "As a summoner spell that affects two champions and gives a movement speed bonus, we've now realized that Heal is pretty strong. Too strong."
- HEAL AMOUNT
95 - 475 ⇒ 90 - 345
"With the removal of Randuin's Omen's passive movement speed debuff, we saw that Heal was giving too much additional safety when a marksmen takes on a fighter, so we're tuning Heal down just a bit. "
- MOVEMENT SPEED BOOST: Speed boost duration now
2 seconds ⇒ 1 second
"When we added more utility to Heal, our focus was to create a spell that added depth to the summoner spell pool while also giving heal-focused supports an ability that let them remain effective against Ignite. On live, however, this wasn't the case as it was primarily being picked up by solo laners to circumvent burst-heavy aggressive play (particularly for champions whose abilities were affected by Grievous Wounds)."
- "REMOVED" GRIEVOUS WOUND CLEANSE: Removes Grievous Wounds
The Heal debuff was something we should have left in when we updated the summoner spell. Without the debuff, there's no real drawback to bringing multiple Heals to a fight instead of an assortment of spells.
- NEW MULTI-HEAL DEBUFF: Heal is 50% less effective on allies previously Healed within the past 35 seconds. This debuff only applies when an ally has been healed by the Summoner Spell Heal.
"While the current live environment heavily favors all-in engagements, we wanted a summoner spell that could be reliably used for defensive lanes. These changes let us expand the scope of Heal so that it has more cool use cases and playmaking opportunities."
300 ⇒ 240
90-345 ⇒ 90-495
- "NEW" UTILITY: Heals all allies in range ⇒ Heals the caster and the allied champion nearest to the caster's cursor (or the most wounded ally if no target is near the cursor)
- "NEW" CRAZY: Removes healing reduction effects on affected champions
- "NEW" CRAZY-AWESOME: Affected champions gain +30% movement speed for 2 seconds
- Heal particles and sound effects updated
- Health restored per level reduced to 15 from 25
- Amount allies are healed for increased to 100% from 50%
- Improved Heal now increases your champion's max Health by 5 per level instead of increasing the Heal amount by 10%
- Cooldown increased to 300 seconds from 270
- Summoner Heal base value reduced to 100 from 145
- Base heal amount reduced to 120 from 140
- Recently Healed debuff duration increased to 35 seconds from 25
- Heal and Clarity summoner spells will now restore health/mana to the caster even if they are untargetable when the summoner spell is cast (Fizz's Playful/Trickster, Vladimir's Sanguine Pool, Zhonya's Hourglass)
- Heal amount per level increased to 25 from 20
- Improved Heal no longer reduces the cooldown but now increases the amount healed by 15%
- Now removes stealth when used
- A debuff is now placed on Champions healed by Summoner Heal for 25 seconds. Subsequent Summoner Heals will have their effect dimished by 50% on allies with the debuff. Your Champion will still receive the full amount of the heal if cast by your Summoner.
- AoE healing reduced from 66% of total to 50%
June 12, 2009 Patch
- Heal now scales with level, health now = 150 x 25 x level and heals surrounding allies from 66% (so it heals less early, and more late)
Alpha Week 4
- Cooldown increased to 5 minutes from 4.5 minutes