It sounds likely that you may be experiencing coronary atherosclerotic disease. Atherosclerosis is manifested with atherosclerotic plaques that narrow the coronary arteries and decreases the blood flow. Plaques are also places susceptible for developing thrombosis which causes sudden blood circulation stoppage and heart attack (infarct). If the process of vessel narrowing goes slowly there is enough time for “back door” (anastomosis) to develop and to compensate for the blockage. People with a condition like yours definitely have certain physical limitations.
Atherosclerosis is a chronic and progressive condition. There are some risk factors that speed this process. Major risk factors are: smoking, high blood pressure, increased blood sugar (diabetes) and increased blood fats. Other risk factors are: male sex, older age, mental stress, overweight, low physical activity, menopause etc. Some factors (sex, age and menopause) can not be influenced but the other factors mentioned can usually be controlled with proper life style changes and medications.