A final receipt, given by an employe or dependent entitled to compensation under a compensation agreement notice or award, shall be prima facie evidence of the termination of the employer's liability to pay compensation under such agreement notice or award: Provided, however, That a referee¹ designated by the department may, at any time within three years from the date to which payments have been made, set aside a final receipt, upon petition filed with the department, or on the department's own motion, if it be shown that all disability due to the injury in fact had not terminated. Where, however, a person is 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 within which a referee may set aside a final receipt upon petition filed with the department, or upon the department's own motion, shall not begin to run until the expiration of the receipt of benefits pursuant to the Heart and Lung Act.