Unstable heart failure is defined as class IV cardiac failure with symptoms that do not respond to empiric treatment, which causes hypotension, renal failure, hyponatremia and/or symptomatic ventricular arrhythmias. It may be reversible or refractory. Refractory or "end-stage" heart failure is an indication for heart transplant, provided that: a) all reversible ethiologic factors have been corrected; and b) aggressive treatment in the intensive care unit under hemodynamic monitoring has not been able to stabilize heart failure.