The effects of optical properties of myocardium tissue due to heating in the visible and near-infrared spectral range were investigated. A spectrophotometer was used to measure the diffuse reflectance and total transmittance of the tissue samples, and the inverse adding-doubling (IAD) method was applied to assess the absorption coefficients, the reduced scattering coefficients and the optical penetration depth of tissue from the measurements. The results of measurement show that the absorption and reduced scattering coefficients and optical penetration depths of myocardium tissues vary with the change of irradiation wavelength. There are a positive peaks at 550 nm for the absorption coefficients of both native and thermocoagulated (treated with 80 ℃) myocardium, and the peak values for native and thermocoagulated myocardium are 0.74 mm-1 and 1.16 mm-1, respectively. There is a positive peak at 550 nm for the reduced scattering coefficients of native myocardium and the peak value is 0.25 mm-1, whereas the peak disappears after myocardium tissue treated with high temperature. Further more a new increase appears at the wavelength range of 590～625 nm. The absorption coefficient of myocardium tissue is not significantly changed by treating with lower temperature but increases slightly with higher temperature. The reduced scattering coefficient of myocardium tissue is significantly increasing with the increase of treating temperature. And the optical penetration depth of myocardium tissue is significantly decreasing with the descrease of treating temperature.