Thrombus. False-colour scanning electron micrograph of a thrombus (blood clot) protruding from an arterial entrance in a chamber of the heart. This type of thrombus, known as coronary thrombosis, is the usual cause of myocardial infarction (heart attack). In the blood there are complex mechanisms which trigger blood clotting in case of damages to blood vessels. At the same time other agents discourage the formation of clots which obstruct the blood flow. In arteries the clotting process may be encouraged by the build-up of atheroma (fatty deposits) on blood vessel walls. Magnification: x120 at 6x7cm size. x190 at 4x5"~LANDSCAPE"