Sentence:  The original electrocardiograph primarily indicates irregularities in the heartbeat , but today 's techniques allow exact measurements of the flow of blood through the <WSD>aorta</WSD> , dimensioning of the heart and its chambers , and a much more detailed study of each heartbeat . 
Meaning of the word marked with <WSD> tags:  the large trunk artery that carries blood from the left ventricle of the heart to branch arteries