Ventricular tachycardia (VT) is a rapid heart rhythm which is often life threatening. Several surgical and percutaneous ways to destroy the myocardium responsible for VT have been studied. It has been postulated that laser therapy may be ideal for this purpose because it can heat a large volume of tissue. Recent developments in diode lasers have prompted us to evaluate this source (810 nm) for photocoagulation of myocardial tissue. Its size, ease of maintenance, and cost make diode laser suitable for clinical practice in general, and for percutaneous photoablation in particular. Lesions were created in myocardium with contact irradiation using a 600 micron bare tipped optical fiber both in vitro and in vivo. Exposures of 2 to 3 W over 30 to 60 seconds created lesions with no or minimal char formations. In vivo lesions tended to be larger than in vitro, with better defined border zones. Animals tolerated laser irradiation well without significant ventricular ectopy. Diode laser irradiation is a promising means to percutaneously coagulate ventricular myocardium and for cure of VT. Further investigation of the dosimetry and healing response in both healthy and diseased myocardium is warranted.