How unhealthy is smoking cigarettes with heart disease?

Very: depends on the kind of heart disease. Smoking is the number 1 preventible cause of arteriosclerosis and coronary heart disease, which are what lead to heart attacks, some strokes and peripheral vascular disease (mostly not getting enough blood in the legs and pain with walking). It is estimated that half of the million or so heart attack deaths in US would not occur if people did not smoke