Your heart is really a muscle that is a pump. The primary purpose is to circulate your blood which is about 2,000 gallons throughout your body. There are four chambers that are involved. You have two upper chambers which are the atria of the heart, and then there are the lower ones called ventricles. The ventricles are responsible for pumping your blood out properly. The valves of the heart separate the chambers. There are four valves that will open and close to send blood flowing properly through the body.
When you have CHF, your heart does not quit beating obviously. What happens though, is that the ventricles, sometimes both, or just one weaken and thus becomes unable to pump aggressively. This causes the blood flow to get behind and, as a result fluid will build up along with the blood with the heart not working properly. You will notice edema in parts of the body, (hands, and feet especially), and as the heart enlarges abnormally, it continues to become weaker over time. This is where failure comes in the heart.
People with diabetes are more likely to have CHF. Diabetes in and of itself is a high risk factor for various heart problems anyway.