A 62-year-old man describes tightness across the chest when he walks up the hill to his home; it settles within three minutes of rest. He first noticed it a month ago, as his stools became black. He looks pale, with pale conjunctivae. The jugular venous pressure is normal and the lung fields are clear.
Heart rate 74 beats per minute Blood pressure 152/84 mmHg Pulse oximetry 98% on room air Haemoglobin 71 g/L
Which one of the following best accounts for the imbalance between myocardial oxygen supply and demand in this man?