38 CFR § 3.312 - Cause of death.
(a) General. The death of a veteran will be considered as having been due to a service-connected disability when the evidence establishes that such disability was either the principal or a contributory cause of death. The issue involved will be determined by exercise of sound judgment, without recourse to speculation, after a careful analysis has been made of all the facts and circumstances surrounding the death of the veteran, including, particularly, autopsy reports.
(b) Principal cause of death. The service-connected disability will be considered as the principal (primary) cause of death when such disability, singly or jointly with some other condition, was the immediate or underlying cause of death or was etiologically related thereto.
(c) Contributory cause of death.
(1) Contributory cause of death is inherently one not related to the principal cause. In determining whether the service-connected disability contributed to death, it must be shown that it contributed substantially or materially; that it combined to cause death; that it aided or lent assistance to the production of death. It is not sufficient to show that it casually shared in producing death, but rather it must be shown that there was a causal connection.
(2) Generally, minor service-connected disabilities, particularly those of a static nature or not materially affecting a vital organ, would not be held to have contributed to death primarily due to unrelated disability. In the same category there would be included service-connected disease or injuries of any evaluation (even though evaluated as 100 percent disabling) but of a quiescent or static nature involving muscular or skeletal functions and not materially affecting other vital body functions.
(3) Service-connected diseases or injuries involving active processes affecting vital organs should receive careful consideration as a contributory cause of death, the primary cause being unrelated, from the viewpoint of whether there were resulting debilitating effects and general impairment of health to an extent that would render the person materially less capable of resisting the effects of other disease or injury primarily causing death. Where the service-connected condition affects vital organs as distinguished from muscular or skeletal functions and is evaluated as 100 percent disabling, debilitation may be assumed.
(4) There are primary causes of death which by their very nature are so overwhelming that eventual death can be anticipated irrespective of coexisting conditions, but, even in such cases, there is for consideration whether there may be a reasonable basis for holding that a service-connected condition was of such severity as to have a material influence in accelerating death. In this situation, however, it would not generally be reasonable to hold that a service-connected condition accelerated death unless such condition affected a vital organ and was of itself of a progressive or debilitating nature.