Mass. Gen. Laws ch. 32 § 94
Notwithstanding the provisions of any general or special law to the contrary affecting the non-contributory or contributory system, any condition of impairment of health caused by hypertension or heart disease resulting in total or partial disability or death to a uniformed member of a paid fire department or permanent member of a police department, or of the police force of the Massachusetts Bay Transportation Authority, or of the state police, or of the public works building police, or to any employee in the department of correction whose regular or incidental duties require the care, supervision or custody of prisoners, criminally insane persons or defective delinquents, or to any permanent crash crewman, crash boatman, fire controlman or assistant fire controlman employed at the General Edward Lawrence Logan International Airport, members of the 104th fighter wing fire department, members of the Devens fire department established pursuant to chapter 498 of the acts of 1993 or members of the Massachusetts military reservation fire department, shall, if he successfully passed a physical examination on entry into such service, or subsequently successfully passed a physical examination, which examination failed to reveal any evidence of such condition, be presumed to have been suffered in line of duty, unless the contrary be shown by competent evidence.
As used in this section the words "permanent member of a police department" shall include a permanent member of the park police of a city or town.
Mass. Gen. Laws ch. 32, § 94