Diagnosis and treatment for the heart and virtually all its structures is becoming available via the pericardium. With or without pericardial effusion (formerly necessary for safe access), instruments that can enter the noneffusive pericardium are available and thoroughly tested experimentally, with human trials currently under way. Successful therapy includes antiarrhythmic, vasodilatory, angiogenic, and other gene-related modalities and agents that stimulate the pericardial mesothelium to exceed the normal production of many active substances.