Sleepycats is right> with the info you provided that is what we could arrive.
But actually, it would be better if provided with more info regarding the reason for encounter, age and the other diagnoses the physician documented.
Blood in the heart could be a thrombus too.
It makes me to ponder a little bit of its etiology and pathophysiology to make the diagnosis more specific
In brief I go:
Blood clots /thrombus can also form in the heart.
In atrial fibrillation, the atrium or upper chamber of the heart does not beat in an organized manner. Instead, it jiggles, and blood tends to become stagnant along the walls of the atrium. Over a time or sooner it can become an embolus/ in the heart
In atrial fibrillation, small clots may form along the walls of the atrium or the upper chambers of the heart. Should one of these clots break off, if can embolize, or travel in the bloodstream to the brain, blocking an artery and causing a stroke, or pulmonary embolism
Other arteries may also be involved by this process, including those that supply the bowel. This can cause mesenteric ischemia (mesentery=lining of the bowel + ischemia=loss of blood supply) and potential necrosis (tissue death) of the intestine.
Blood should clot anytime it becomes stagnant.
So the underlying patholgy would help us to get to the specific diagnosis.
Moreover blood in the atrium is a finding at electro/echo / US/ MRI findings which were done after an underlying condition as a reason to perform like I said Atrial Fibrillation, storke, Pulmonary Embolism
etc etc .
Thank you