MSRA-0032

A 65-year-old man was diagnosed with angina after experiencing chest pain during physical activity. He underwent an exercise test at the cardiology clinic and was prescribed aspirin, bisoprolol, atorvastatin, and a glyceryl trinitrate (GTN) spray.
After six months, he returned with an increase in the frequency of anginal episodes, which were relieved by GTN spray and did not occur at rest.
What medication would be the most suitable addition to his current treatment?