In cases of personal injury all claims for compensation shall be forever barred, unless, within three years after the injury, the parties shall have agreed upon the compensation payable under this article; or unless within three years after the injury, one of the parties shall have filed a petition as provided in article four hereof.¹ In cases of death all claims for compensation shall be forever barred, unless within three years after the death, the parties shall have agreed upon the compensation under this article; or unless, within three years after the death, one of the parties shall have filed a petition as provided in article four hereof. Where, however, in the case of any person receiving benefits pursuant to the act of June 28, 1935 (P.L. 477, No. 193), referred to as the Heart and Lung Act,² the two-year period³ in which parties must agree upon the compensation or file a petition for compensation in cases of personal injury or in death, shall not begin to run until the expiration of the receipt of benefits pursuant to the Heart and Lung Act. Where, however, payments of compensation have been made in any case, said limitations shall not take effect until the expiration of three years from the time of the making of the most recent payment prior to date of filing such petition: Provided, That any payment made under an established plan or policy of insurance for the payment of benefits on account of non-occupational illness or injury and which payment is identified as not being workmen's compensation shall not be considered to be payment in lieu of workmen's compensation, and such payment shall not toll the running of the Statute of Limitations. However, in cases of injury resulting from ionizing radiation in which the nature of the injury or its relationship to the employment is not known to the employe, the time for filing a claim shall not begin to run until the employe knows, or by the exercise of reasonable diligence should know, of the existence of the injury and its possible relationship to his employment. The term “injury” in this section means, in cases of occupational disease, disability resulting from occupational disease.