Someone finally wrote the tool I've been dreaming of! WowCardioRaid takes a WoW combat log and renders it as a timeline, showing you graphs of people's health and little dots for important events.
Above is a graph of me tanking Halazzi, the Zul'Aman boss famous for doing scary spiky damage. I've never had a lot of trouble tanking him as a bear, but looking at this graph gives me a new appreciation of the healing challenge. I fiddled with the program settings quite a bit to get a graph that's focussed on damage and heals to me (the main tank). The story is quite a little drama.
First thing to look at is the little green line for me, Flyv. That's my health during the fight. I'm well over 50% of health most of the time except right at the end when I dip to 10%. Scary! You can also see the health for my companion tank Pepped; he's helping out with Saberlashes and tanking the Spirit Lynx add and gets pretty low there a few times. And you can also see the health for the rest of the raid, including the periodic damage people take everytime Halazzi splits and the unfortunate death of Blessing, our shadow priest. (Last damage event was Shadow Word: Death. Oops.) Finally you can see Halazzi's health at the bottom. The sawtooth pattern is not typical of a boss, but Halazzi respawns at full health three times during the fight.
The next thing to look at are the little dots. I used the tool to filter it so it shows dots for four things. White is melee damage from Halazzi, yellow is spell damage from Halazzi, bright green is direct heals on Flyv and dark green is HoTs on Flyv.
Focussing first on the damage, if you look at Halazzi's line you can see a sequence of white dots for his melee attacks. That's your basic combat damage, no big deal. The yellow dots are scarier; those represent his Transfiguration damage to the whole raid as well as Saber-Lashes to the two tanks. You can see the correlations between three of the yellow dots and the whole raid taking damage. There's also Saber-Lashes; it's this spike damage that makes that fight hard on the tank healers. I managed to dodge most of them, but had a string of bad luck in the middle of the fight. And the scary dip at the end is where I happened to take a bunch of melee hits in a row combined with a Saber-Lash (a big one; 6240 damage).
Finally you can look at how the healers healed me during the fight. Our two main healers were Menstumper (paladin, direct heals) and Tracewind (druid, HoTs). There's also a lot of healing incoming from Blessing (shadow priest) and from myself (Improved Leader of the Pack, Lifeblooms popping, and a string of Frenzied Regeneration ticks).
My favourite part of the graph is the two direct heals that came from Pepped, right at the end of the fight when I was about to die. My brother tank saved my life! That last heal is actually a Lay on Hands, an enormously powerful ability. Quick thinking may well have saved our raid.
So that's a quick example of the WowCardioRaid tool. It's got some rough edges in the UI, still a new program, but it's already immensely powerful and fun to play with.