Gribben worked for UPS. He claimed a heart condition was a "disability" because it "substantially limited" major life activities. Specifically, Gribben's physician felt that he could not perform a lot of physical activity when temperatures rose above 90 degrees. (The problem was that Gribben lived in Phoenix.)
The district court granted summary judgment against Gribben because he did not show that he had more trouble with physical activity in the hot Phoenix weather than a person without a disability. The Ninth Circuit reversed, holding Gribben's testimony about his own limitations was enough to raise a triable issue of fact.
Whether or not you have a heart condition, it becomes harder to physically exert oneself in hot summer sun. So, how can you tell if a condition is "substantially limiting" without some basis for comparison? I guess the court's point is that the comparison can be made by the fact finder rather than the trial court on summary judgment.
The case is Gribben v. UPS and the opinion is here.