A 64 year old man had received a Medtronic-Hall aortic valve prosthesis eight years previously. During follow up the systolic gradient across the valve prosthesis had increased from 32 to 68 mm Hg without symptoms. He was now admitted with acute shortness of breath. On admission he was dyspnoeic, his pulse was 68 per minute and regular, and his blood pressure was 100/60 mm Hg. The clicks of the prosthetic valve were normal, and a systolic ejection murmur was unchanged. Intermittently the murmur of aortic insufficiency was heard. The ECG showed sinus rhythm and a left bundle branch block, unchanged from previous tracings. A therapeutic international normalised ratio (INR) of 3.9 was documented. Doppler echocardiography showed beats without aortic insufficiency (panel A) and intermittent beats with severe aortic insufficiency (panel B, arrow 1). The continuous wave recording (panel C) showed beats in which initial aortic insufficiency was seen, abruptly interrupted by a click (arrow 2) and beats with holodiastolic aortic insufficiency (arrow 3). The diagnosis of valve obstruction caused by pannus formation and intermittent regurgitation from impaired valve closure was confirmed during surgery. The valve was replaced. Pathologic examination of the specimen showed mixed fibrotic tissue and organised thrombus. The patient recovered well from surgery.