The info already given is good. Basically a heart attack occurs when blood cannot reach the heart. As blood carries oxygen, the heart muscles become ischaemic (literally "without blood"), anaerobic respiration must occur, producing lactic acid which is essentially a poison, and some cells within this muscle die, causing the constricting feeling in the chest. This normally occurs due to a blockage in an important blood vessel - plaques build up on the surface of the veins and arteries, and they originally get there due to high blood pressure damaging the delicate surface of the vessel, causing physiological changes which lead to the surface becoming hardened - this is called atherosclerosis, literally meaning "hardening of the arteries". Anything which will cause the blood pressure to rise can trigger a heart attack if the blockage is significant enough - this may be cholesterol from smoking and unhealthy diet narrowing the space within the vessel for the blood to pass through, or an unusual amount of stress causing the heart to beat faster so that a bigger volume of blood is trying to pass through the vessel. If your dad is still alive and kicking then chances are the heart attack was fairly minor. By keeping him in hospital you can be assured that he will be under constant surveillance and will be given anticoagulants - blood-thinning drugs - and kept nice and calm so that his blood pressure does not rise dangerously again. He will also have access to fresh oxygen and his diet will be carefully controlled so that he is not eating too much cholesterol or salt. So the fact that he is staying in hospital should give you peace of mind, not cause for concern, as his condition can be controlled and if anything does go wrong he will get immediate help. In terms of reoccurrence, he will be strongly advised to re-evaluate his lifestyle: to take more exercise, eat a healthier diet, lose weight, ingest less salt and quit smoking. He will probably also be provided with medication to reduce the clotting mechanism in his blood and lower his cholesterol levels. I hope this information puts your mind at rest a little. Although a heart attack sounds really scary, they are not always fatal by any means and if he has survived this one easily then chances are he will never have another one as it will give him the wake up call he needs to change his attitude to his body. In terms of your mum, I expect she feels exactly the same as you so maybe get her to read up on the subject so she feels more informed and less out of control. Be there for each other and I'm sure your dad will be home in no time, then you can both concentrate on getting him properly well again.