Pericardial (around the heart) effusion (fluid collections) after heart surgery are very common. Some patients have trivial ones which require simple monitoring and follow up and they typically resolve over time. Other develop larger collections which may make it harder for the heart to work. They may also cause atrial arrhythmias (fast heart rates) for which patients have higher perdisposition anyway after major surgery. When the collection is large we typically remove it with a procedure known as pericardiocentesis where a needle is inserted into the pericardial cavity and a drain is placed for up to 24 hours. If the fluid does not recur after a few days, then patients are ok to go home. On the other, in some patients, the fluid does reaccumulate and a more permanent procedure known as pericardial window is performed to drain the fluid. Again this is very common after heart surgery. The atrial arrhythmia (HR 160) is also common after surgery. In your father it may be related to the fluid collection around the heart. Taking it out might help. The arrhythmia typically resolves within a month after the original operation. Depending on your dad's age and risk factors for developing atrial fibrillation he may have it permanently and require medications and even blood thinners to treat it.
thanks for the clarification