<s>[INST] Hi, my spleen has been pulsating for about a day now, almost like an irregular heartbeat. The area is tender and stiff as well. I had a severe case of mono in January, and I was wondering if that's what it could be? Though it's a different feeling than when I had mono. [/INST] Hi, I had gone through your question and understand your concerns.This is pretty unusual symptom and I am not sure if this is caused by spleen issue. This may be an aorta puslating as we can see in aortic aneurism. However, splenomegaly may occur as a consequence of mono infection and this is known mechanism. SO it would be good:1. to do ultrasound and measure spleen size and presence of aortic aneursim2. do liver and lab tests including presence of Ebstein bar antibiodies3. Do heart ultrasound to check for arrihmiasAfter you do these tests, the condition will be more clear and further treatment depends on it. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Wishing you good health. </s>