has discarded, among others, the concept of presumption of compensability and aggravation and substituted one based on social security principles . The new system is administered by social insurance agencies the GSIS and the SSS under the ECC.The purpose of this innovation was to restore a sensible equilibrium between the employers obligation to pay workmens compensation and the employees right to receive reparation for work-connected death or disability. [ 1 0 ]  (Emphasis supplied)   There is no dispute that Rheumatic Heart Disease is not included under the P.D. No. 626, as amended, as an occupational disease.Hence, under P.D. No. 626, as amended, the employee must demonstrate through substantial evidence (1) that the risk of contracting the disease was increased by the claimants working conditions, and (2) the causal relation between the ailment and working conditions.   The petitioner correctly points out that the respondent failed to discharge his burden of proof. The Certifications of the Department of Health bear no relevance to the claims of the respondent for a number of reasons. First, the Certifications clearly state the purpose and period for which it may used, i.e., for the purpose of claims for hazard pay and for the years 1995 and 1996 only, thus indicating that the conditions may not necessarily exist before or after 1995 or 1996; and, second, the Certifications show that he had been exposed to toxic chemicals and biological hazards but do not go any furtherthey do not indicate the causal relation between the exposure and Rheumatic Heart Disease.   In its Decision, the ECC, quoting medico-legal authorities, explained the nature of Rheumatic Heart Disease, thus:   x x x either resulted from or ascribed to previous rheumatic fever. With the declining incidence of acute rheumatic fever, other etiologies are increasingly recognized; congenital defects that may become apparent until late childhood or adult years, myxomatous,  scleroris  and calcifications.  Whatever the