• Atrial fibrillation
• Ventricular rate 75-200/min
• Normal axis
• Normal QRS complexes
• Downward-sloping ST segment depression, especially in leads V5, V6

The ventricular rate is not adequately controlled, though the ST segment depression suggests that he is taking digoxin. There are no changes to suggest ischaemia.

In the absence of clinical or ECG evidence of ischaemia, possible diagnoses include rheumatic heart disease, thyrotoxicosis, alcoholic heart disease, and other forms of cardiomyopathy.
Echocardiography is necessary. The serum digoxin level must be checked and the digoxin dose increased if appropriate. In addition to digoxin, the patient will need an angiotensin-converting enzyme inhibitor, a diuretic and, probably, anticoagulants. Beta-blockers must be considered once his cardiac failure is controlled.