Okla. Stat. tit. 85A, § 14

A. A cardiovascular, coronary, pulmonary, respiratory, or cerebrovascular accident or myocardial infarction causing injury, illness, or death is a compensable injury only if, in relation to other factors contributing to the physical harm, the course and scope of employment was the major cause. B. An injury or disease included in subsection A of this section shall not be deemed to be a compensable injury unless it is shown that the exertion of the work necessary to precipitate the disability or death was extraordinary and unusual in comparison to the employee's usual work in the course of the employee's regular employment, or that some unusual and unpredicted incident occurred which is found to have been the major cause of the physical harm.