A 68-year-old man comes to the office for routine follow-up of stable angina. He reports that he experiences substernal chest pressure when climbing two flights of stairs to his apartment. The discomfort resolves within 2-3 minutes after he stops and takes one sublingual nitroglycerin tablet. He has a history of an inferior wall myocardial infarction 5 years ago treated with percutaneous coronary intervention. He takes aspirin, metoprolol, atorvastatin, and sublingual nitroglycerin as needed. His temperature is 37.0°C (98.6°F), pulse is 62/min, and blood pressure is 138/82 mm Hg. Physical examination shows no jugular venous distension. Cardiac examination shows a regular rate and rhythm with no murmurs, rubs, or gallops. The lungs are clear to auscultation bilaterally. There is no peripheral edema. An ECG shows sinus rhythm with Q waves in leads II, III, and aVF.
Which of the following hemodynamic changes best explains the mechanism by which nitroglycerin relieves this patient's symptoms?