TMLR (Transmyocardial Laser Revascularization) has been introduced to treat severe coronary artery disease that cannot be treated by conventional treatments such as PTCA (percutaneous transluminal coronary angioplasty) or CABG (coronary artery bypass grafting). TMLR is a laser-ablation-based surgical procedure in which laser channels are created through the myocardium to increase the flow of blood in the oxygen-starved tissue, thereby relieving angina and debilitating symptons of coronary artery disease. For this treatment, a high-power 10.6-μm CO2 laser has been mainly used to create the channels. Recently, however, a variety of lasers including 2.1-μm Ho:YAG and 308-nm XeCl excimer lasers have appeared to be applied. Although many clinical results are reported, no comprehensive study has been, so far, performed to reveal the optimum laser irradiation conditions for this treatment. The authors investigated the dependence of the irradiation wavelength on the ablation characteristics of the myocardial tissue in the UV (ultraviolet) spectral region, where damage-free ablation was expected. As a light source for ablation, the authors used a tunable OPO (optical parametric oscillator).