Weiss, P.J.
Claimant suffered serious injuries to his right leg, hip and spine on February 18, 1988 which required a laminectomy for a herniated disc. A second laminectomy was necessary and was performed on May 11, 1989. Claimant had a preexisting but dormant heart condition, which, during his 22 years of work as a laborer involving much heavy lifting, disabled him only once for a brief period in 1985. Against this background the employer and its insurer challenge the Workers' Compensation Board's determination that claimant's disabilities result solely from his back injury.
The record contains substantial evidence supporting the Board's determination that claimant's permanent disability was not made materially or substantially greater because of his preexisting heart condition (see, Workers' Compensation Law § 15 [d]). It is the prerogative of the Board to resolve factual disputes created by conflicting medical opinions (Matter of Biller v State Ins. Fund, 186 A.D.2d 300, 301). The record further supports the finding that claimant was totally disabled for the period of August 15, 1988 to May 11, 1989.
We find the insurer's remaining contention to be without merit. The Board's decision reflects an appropriate application of the Workers' Compensation Law § 15 (8) (d) standard.
The employer's argument concerning a contractually based reimbursement claim was not addressed administratively nor was it presented in proceedings before the Board, and therefore may not be raised for the first time on this appeal (see, Matter of Middleton v. Coxsackie Correctional Facility, 38 N.Y.2d 130).
Yesawich Jr., Levine, Mercure and Mahoney, JJ., concur. Ordered that the decision is affirmed, with one bill of costs.