A 75-year-old man is brought to hospital with an episode of dizziness. He still feels unwell when he is seen 30 min after the onset. He was well until the last 6 months, since when he has had some falls, irregularly. On some occasions he lost consciousness and is unsure how long he has been unconscious. On a few occasions he has fallen, grazing his knees,and on others he has felt dizzy and has had to sit down but has not lost consciousness. These episodes usually happened on exertion, but once or twice they have occurred while sitting down. He recovers over 10–15 min after each episode. He lives alone and most of the episodes have not been witnessed. Once his granddaughter was with him when he blacked out. Worried, she called an ambulance. He looked so pale and still that she thought that he had died. He was taken to hospital, by which time he had recovered completely and was discharged and told that he had a normal electrocardiogram (ECG) and chest X-ray. There is no history of chest pain or palpitations. He has had gout and some urinary frequency. A diagnosis of benign prostatic hypertrophy has been made for which he is on notreatment. He takes ibuprofen occasionally for the gout. He stopped smoking 5 years ago.He drinks 5–10 units of alcohol weekly. The dizziness and blackouts have not been associated with alcohol. There is no relevant family history. He used to work as an electrician.ExaminationHe is pale with a blood pressure of 96/64 mmHg. The pulse rate is 33/min, regular. There are no heart murmurs. The jugular venous pressure is raised 3 cm with occasional rises. There is no leg oedema; the peripheral pulses are palpable except for the left dorsalis pedis. The respiratory system is normal. What is the diagnosis and what are your reasons?