Complications of any mechanical prosthesis include thrombus or pannus formation. In our case report we demonstrate that prosthetic aortic valve regurgitation due to pannus formation may be intermittent and non-cyclic in pattern and therefore not obvious at the time of original clinical examination. Under these conditions and as transesophageal echocardiography cannot be repeated promptly, transthoracic 2-D and Doppler echocardiography should be available at any time when symptoms occur and present the method of choice for acute patient evaluation. Thrombolysis seems to be the first treatment of choice in case of thrombus formation and re-do surgery in case of pannus formation.