The situation is very comparable to our daily living. How much money we have at the end of the month depends upon income and expenses. If our income decreases, to maintain the same lifestyle, we have to increase our income from another source. If that cannot be done, we have to cut back on our lifestyle by reducing expenses. In the case of the heart, income can be equated to blood flow bringing in the necessary oxygen.
Drugs are available to increase that blood flow by dilating the coronary arteries.
High blood pressure would be an example of an increased work load. Most drugs used for the treatment of coronary artery disease either reduce the work load on the heart, or they increase the blood supply. How effective one approach is compared to another depends entirely on the clinical situation. As a general rule, work load reducing drugs tend to be more effective than medications that increase the blood flow to the heart muscle.