Light micrograph of a section of human heart muscle (myocardium) from the left ventricle, showing a calcified embolus lodged in a coronary artery. The embolus appears as the densely-stained purple object occupying the left-side part of the interior of the artery. Surrounding the obstructed artery are pink-staining heart muscle fibres. Sources of emboli in the coronary arteries are from blood clots following myocardial infarction (a heart attack), the death of a section of heart muscle due to an interruption in its blood supply. Magnification: x70 at 6x7 size, x40 at 35mm size.