Pulmonary embolism. Coloured computed tomography (CT) angiography scan of the chest of a patient with blood clots in the pulmonary artery. The pulmonary artery carries blood to the lungs and the embolism is greatly reducing the blood flow. Smaller clots may cause shortness of breath, dizziness and chest pain. Larger clots can be fatal, as the blood is quickly starved of oxygen. Thrombolytic drugs can be used to break up a clot, and anti-coagulant drugs may help prevent the formation of others.