The three transport equation optical properties, the absorption coefficient, the scattering coefficient, and the average cosine of the scattering angle, or anisotropy factor have been measured (at 632.8 nm) for canine myocardium after it is heated in a water bath at room temperature and at 37-75 degrees C for 1000 s. The measurement system was a double integrating sphere with collimated light and utilized the adding-doubling solution to the equation of radiative transfer. The absorption coefficient (room temperature control, 2.0 +/- 0.4 cm(-1)) began to increase and the anisotropy factor (room temperature control, 0.93 +/- 0.02) to decrease at above 45 degrees C. At 75 degrees C the changes were significant at the p < 0.0005 level (absorption, 4.5 +/- 1.3 cm(-1); anisotropy, 0.78 +/- 0.05). There was no significant change in the scattering coefficient (room temperature controls, 161 +/- 33 cm(-1)).