Correct answer: b) Left atrium
The chamber with filling defect marked by red arrow is just anterior to the spine and is hence the left atrium. The chamber anterior and to the right of it is the right atrium. Left ventricle is the largest chamber seen anteriorly and to the left of the left atrium. Right ventricle is seen retrosternally.
Negative shadow is due to the thrombus in the left atrium.
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