Human arterial segments with occlusive defects and acute dog hearts were exposed, in vitro, to high-energy pulsed and continuous wave (CW) laser beams at argon (514 nm) and Nd-YAG (1,064 nm) wavelengths, using various pulse powers, durations and pulse repetition rates. The laser effects included vaporization of plaques in the arterial segments and penetration of the pericardial sac, evaporation of pericardial fluid, and discoloration of tissue with crater-like lesions in the impact zone, all as a result of vaporization of heart muscle tissues. The areas affected and depth of penetration depended on the wavelength, power, pulse duration, and mode of energy deposition. Focused nanosecond Nd-YAG laser pulses at repetition rates of 40-50 Hz caused ablation or vaporization of hard plaques and kidney stones in air and saline. Picosecond (mode-locked) argon laser pulses at repetition rates of 3.8 MHz--average power 6.5 W, peak power of 230 W--caused effective vaporization of hard plaques and kidney stones in air and saline. Picosecond argon laser pulses--average power 1 W, peak power 250 W--were not effective in vaporization. Transmission characteristics of the various types of laser pulses through fiber optic waveguides were determined. The energy and power density required to vaporize fatty and hard plaques and kidney stones were tabulated as a function of laser wavelength, pulse energy, duration, and repetition rates.