Abstract: Devices, systems and methods are provided for treating conditions of the heart, particularly the occurrence of arrhythmias. The devices, systems and methods deliver therapeutic energy to portions the heart to provide tissue modification, such as to the entrances to the pulmonary veins in the treatment of atrial fibrillation. Generally, the tissue modification systems include a specialized catheter, a high voltage waveform generator and at least one distinct energy delivery algorithm. Other embodiments include conventional ablation catheters and system components to enable use with a high voltage waveform generator. Example catheter designs include a variety of delivery types including focal delivery, “one-shot” delivery and various possible combinations. In some embodiments, energy is delivered in a monopolar fashion. However, it may be appreciated that a variety of other embodiments are also provided.