Abnormalities of mental function are common problems in patients with congestive heart failure, a problem that is often referred to the consulting psychiatrist. These abnormalities become more frequent and more serious as failure of the heart progresses and they can exhibit a wide variety of manifestations. Cardiac output and cerebral blood flow are preserved due to compensatory mechanisms in mild heart failure but can be severely compromised in advanced failure. Drugs used to treat heart failure, especially digitalis, can produce a wide variety of mental aberrations including delirium, usually when these drugs are used in excess. Diuretics can produce electrolyte abnormalities resulting in mental derangements and vasodilator therapy can produce hypotension. Psychotropic drugs are well recognized as having significant cardiovascular effects that need to be considered when these agents are applied to the cardiac patient. Antidepressant and antipsychotic drugs have anticholinergic, antiadrenergic and quinidine-like effects that can produce further cardiac decompensation in heart failure. Antidepressants are generally well tolerated except when toxic levels occur or in the most extremely compromised cardiac patients. Monoamine oxidase inhibitors should be used only in highly reliable patients to avoid the acute hypertensive crises that are well known to occur with these agents. Antipsychotic drugs with limited cardiovascular side effects can be used effectively and safely but care must be taken to avoid toxic levels which could produce excess hypotension or lethal arrhythmias. Lithium can also be used in heart failure if patients are effectively monitored to avoid toxic levels which could occur due to reduction in renal function, use of diuretics or imposition of a low sodium chloride diet. Evaluation and management of patients with mental symptoms and heart failure provides a strong challenge for the consulting psychiatrist.