Two years later, Mr Garcia attends his doctor complaining of episodes of chest discomfort. He reports that at first, he noticed the discomfort when he experienced extreme exertion, such as running for the bus. He remembers that the symptoms subsided quickly upon rest. He attributed this to just getting old, more than anything. However, he is more concerned now because the chest pain episodes have become more frequent (at least twice a week) and are brought on with less strenuous activity like walking up a flight of stairs. They still resolve with rest.  

What is the most appropriate drug for Mr. Garcia?