In DVT, there is the potential danger of a blood clot breaking free and travelling with the blood stream. As a consequence, the clot is able to reach the heart. From there, it can be transported to the arteries of the lungs, where it may become stuck in the smaller vessels, causing a pulmonary embolism (PE).

References:
Goldhaber SZ, Morrison RB. Pulmonary Embolism and Deep Vein Thrombosis. Circulation 2002; 106: 143638

Spencer FA, Emercy C, Lessard D, et al. The Worcester Venous Thromboembolism study: a populationbased study of the clinical epidemiology of venous thromboembolism. J Gen Intern Med. 2006; 21: 72227

Goldhaber SZ. Pulmonary Embolism. N Engl J Med 1998; 339: 93104

Prandoni P, Lensing AW, Cogo A, et al. The longterm clinical course of acute deep vein thrombosis. Ann Intern Med 1996; 125(1): 17