Obstructive prosthetic valve thrombosis is a serious complication in patients with prosthetic heart valves. It should be suspected in patients with worsening functional class, embolic phenomena, and inadequate anticoagulation. TTE is very informative and the most frequent modality to begin with. TEE is extremely important, with its unique role in excluding high-risk thrombi. Fluoroscopy is currently the best modality for the assessment of leaflet motion, especially for the aortic position, while cardiac CT may be of added value due to its unique post-processing features. Efforts to discriminate thrombosis from pannus should be made, although current methods are frequently inconclusive. The application of 3-dimensional TEE is hoped to improve the diagnostic accuracy further. Once the diagnosis is established, therapy should be offered according to the local expertise, considering the risk of surgery, the risk of thrombolysis (mainly—bleeding and embolism), the patients' functional class, and the likelihood of achieving valve reopening. Guidelines are numerous and puzzling. Thrombus size is probably the most important determinant of complications, and if it is small, thrombolysis is probably advised across all degrees of functional class, as suggested by American College of Chest Physicians.