Your heart is a muscle. Exercising your heart is the same as exercising other muscles. By increasing the demand on it during exercise, you make it bigger and stronger. Just like doing pushups.
A bigger and stronger heart means it can push blood easier. If you exercise for 30-90 minutes a day, your heart has an easier time for the remaining 22.5-23.5 hours in the day.
Exercise boosts high-density lipoprotein (HDL), or "good" cholesterol and decreases unhealthy triglycerides. This will help your blood flow easier, and reduce the risk of future cardiovascular disease.
Exercise can aid in weight loss.
Exercise will give you more energy and improve your metabolism.
Exercise will make it easier to fall asleep at night.
It will improve your respiratory system. You will be able to get oxygen to your muscles easier. If a walk to the mailbox or walking up the stairs used to make you feel winded, that feeling will improve over time.
Exercise induces your body to increase your mitochondrial density. Mitochondria are cellular structures that function as power plants in the cells. Mitochondria burn carbs and amino acids and fatty acids for energy and give ATP which is the cellular form of energy which is used by cellular processes throughout the body. More is better with mitochondria.
Capillaries supply blood and oxygen to muscles and remove waste. Exercise can lead to increases in capillary density and improved capillary function.
Having an exercise program will keep you from driving your wife nuts after you retire.
Exercise will improve your mood.
I will help you with everything but the motivation, because finding it yourself works better.