Final answer:
The claim on Granville's insurance policy was most likely denied because it was an Accidental Death and Dismemberment policy, which does not cover natural causes of death such as heart attacks.
Step-by-step explanation:
The most likely reason Granville's insurance claim was denied after his passing from a heart attack could be that it was an Accidental Death and Dismemberment (AD&D) policy. AD&D policies typically only pay out in cases of accidental death, not natural causes like a heart attack. If Granville had a condition that was excluded due to it being a pre-existing condition, then that could also be a factor. However, the scenario provided does not directly mention such an exclusion. Innocent misrepresentation or a reduction provision might also lead to claim denial, but these are less likely in comparison to an AD&D policy exclusion.