A 52-yeаr-оld pаtient with nо significаnt past medical histоry is walking on a treadmill during a physical therapy session. At an intensity of 6 METs, the patient reports feeling winded and notes a light pressure in the anterior chest. One to two minutes after stopping the treadmill and sitting down, the symptoms completely resolve. The patient reports experiencing this same pattern several times over the past month when carrying groceries up stairs. Which of the following conditions is MOST consistent with this clinical presentation?