In lieu of all amounts ordinarily contributed by an employee and by the city for age and service annuity, and widow’s annuity the city shall contribute sums equal to such amounts for any period during which the employee receives a duty disability benefit under this Article, or a temporary total disability benefit under the Workers’ Compensation Act if the disability results from a condition commonly termed heart attack or stroke or any other condition falling within the broad field of coronary involvement or heart disease, to be credited to the disabled employee for annuity purposes as though he were in active discharge of his duties during any such period of disability.