Postoperative Hypertension or Volume Overload: Recent surgery can lead to fluctuations in blood pressure and fluid status, potentially causing a new heart murmur due to increased flow across the heart valves.

Aortic Stenosis: A common valvular heart disease in the elderly, which can become more pronounced or symptomatic post-surgery due to changes in hemodynamics.
Mitral Regurgitation: Can be exacerbated by postoperative changes in cardiac function or volume status, leading to a new or worsened murmur.
Tricuspid Regurgitation: Often associated with pulmonary hypertension, which can be exacerbated by the stress of surgery, leading to a new onset murmur.

Endocarditis: Although less common, endocarditis is a critical diagnosis to consider, especially in the post-surgical period, as it can be life-threatening if not promptly treated. The new murmur could be a sign of valve involvement.
Prosthetic Valve Dysfunction (if the patient has a history of valve replacement): If the patient has a prosthetic valve, dysfunction of the valve could present as a new murmur post-surgery.
Pulmonary Embolism: While not directly causing a heart murmur, significant pulmonary embolism can lead to acute right heart strain, which might be misinterpreted as a new murmur, and is a critical condition to rule out post-surgery.

Cardiac Tumor (e.g., Myxoma): Although rare, cardiac tumors can cause new murmurs by obstructing blood flow or interfering with valve function.
Traumatic Injury to the Heart: If the surgery involved the chest or there was significant trauma, a rare but possible cause of a new murmur could be direct injury to the heart or its valves.
Marantic Endocarditis: Associated with malignancy and can cause non-bacterial thrombotic endocarditis, leading to valve dysfunction and new murmurs, though this is less common.