Appeal from a decision of the Workers’ Compensation Board, filed March 23, 1979. Substantial evidence supports the finding that claimant’s disability is compensable as the result of a work-related accident. In attacking thé board’s determination, the self-insured employer criticizes the testimony of claimant’s expert medical witness and maintains that claimant did not sustain a myocardial infarction following strenuous efforts while fighting a fire on November 29,1977. While the validity of the opinion given by that witness was questioned on cross-examination, he clearly stated the reasons for his view and it was for the board to decide whether it should be accepted. The opinion he expressed was not speculative (cf. Matter of Beltran v Allied Maintenance Corp., 45 AD2d 795) and the board was free to prefer it over the contrary medical evidence developed by the employer (Matter of Currie v Town of Davenport, 37 NY2d 472). Decision affirmed, with one bill of costs to respondents filing briefs. Mahoney, P. J., Greenblott, Sweeney, Kane and Casey, JJ., concur.