Heart disease is the biggest killer in the world .If you make a fist and put it on the middle of your chest with the thumb up , you will get an idea of the shape of the heart .From the top ie thumb part comes out a big pipe , called the aorta , which curves up and then goes behind the heart and splits into two , one pipe goes up to the head and the other two the legs. 
Just after the aorta comes from the heart it gives off three tiny pipes , called the coronary arteries , see Fig 1

which go along the surface of the heart and supply the muscle of the heart underneath . There is one in front called the left anterior descending artery and one going round to the back of the heart ( not shown) called the left circumflex and one to the right heart called the right coronary artery .If these arteries block up then the part of the heart supplied by them dies , ie one suffers a heart attack . Too much damage and it can kill . Even a little damage if it affects the part where the nerves of the heart lie , can cause it to beat irregulary or like a quivering jelly but without contracting properly , ie ventricular fibrillation and lead to death . What causes these arteries to block up and can it be prevented ? The main cause is a fat called cholestrol being deposited in the lining of the pipes which narrows the pipe and eventually a blood clot can block it .Similar blockages in brain arteries cause strokes . It has been discovered that the following cause increased deposition of cholestrol in the pipes.. 1. High blood cholestrol levels due to a high cholestrol diet. 2. Inability to break down the blood cholestrol due to genetic defects . 3. High blood pressure. 4. Diabetes 5. Smoking 6. Low thyroid hormones 7. To a minor extent overweight esp around the waist , too much alcohol , stress 8. Rarer causes Those things that protect the heart are 1. Moderate alcohol eg red wine 2. Excecise , 20 minutes three times a week enough to make one sweat ,which build up the good cholestrol to combat the bad type 3. Cholestrol lowering drugs to push it below 5 if possible to be continued 4.Hormone replacement therapy