Delivery systems for accessing the targeted tissue within the living being and introduction of at least one agent at select locations into the tissues of the heart such as the myocardium and other select tissues. Where appropriate, portions of the system are steerable to properly orient the device. When tissue penetration is utilized, the device may include a feature to control the depth of penetration. removal. The system may utilize some form of mechanical action or application of energy (e.g. electrical, sonic, thermal, optical, pressurized fluid, radio frequency (RF), nuclear) in the process. The agent delivered to the tissue may include one or more of pharmaceuticals, biologically active agents, radiopaque materials, etc.