Morrowind:Heart Ring

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Artifact: Heart Ring (heart ring)
Type	Ring
Statistics
Weight	0.2	Value	30,000
Enchantment
Cast When Used     Dispel 20−50% on Self     Lightning Shield 10−20 pts for 30 secs on Self     Resist Frost 30−50% for 30 secs on Self     Resist Fire 30−50% for 30 secs on Self     Resist Magicka 30−50% for 30 secs on Self     Resist Shock 30−50% for 30 secs on Self     Resist Paralysis 30−50% for 30 secs on Self
Charge/Cost = Uses		2,840/568 = 5

Laying in the Facility Cavern of Citadel Dagoth Ur together with Dagoth Ur himself, whom you'll have to kill during the assault on Dagoth Ur at the end of the Main Quest.

Note: There is a second Heart Ring listed in the Construction Set, ID: artifact_heart_ring. It has a weaker enchantment, missing the Magicka, Shock, and Paralysis resists, and the durations of the effects are all set to 0 for some reason. Needless to say, this item is not very useful.