The cardiovascular and renal systems are responsible for maintaining fluid and electrolyte balance in vertebrates. In animals suffering from congestive heart failure, extracellular fluid volumes expand in response to increased capillary hydrostatic pressures leading to edema and tissue congestion. Management of the patient with heart failure often involves treatment with one or more therapeutic agents to improve cardiac performance and circulatory hemodynamics. In addition to cardiovascular drugs, diuretic agents are often administered to aid in reducing the edema associated with congestive heart failure. Cardiac arrhythmias can also disrupt hemodynamic functions which, if left untreated, can lead to the death of the victim. Stabilization and restoration of the normal rhythm of the heart may be accomplished by the judicious use of antiarrhythmic drugs. This group of agents also includes the hemostatic and anticoagulant drugs. The cardiac glycosides include ouabain, digitoxin, digoxin, digoxigenin, and digitoxigenin.