Sinus of Valsalva aneurysms (SOVA) are rare anomalies which often only become apparent at the time of rupture. Syncope associated with unruptured aneurysms is a recognized symptom but in most previously reported cases the mechanism has been either a brady- or tachyarrhythmia. We report a case of a large SOVA affecting the right coronary cusp which presented with syncope secondary to hypotension thought to be resulting from reduced left atrial filling as a consequence of transient right ventricular outflow tract (RVOT) obstruction. The case demonstrates how echocardiographic and angiographic images correlate and also an unusual mechanism of syncope. SOVA are rare anomalies that often only become apparent at the time of rupture. Syncope associated with unruptured aneurysms is a recognized symptom but in most previously reported cases the mechanism has been either a brady- or tachyarrhythmia. We report a case of a large SOVA affecting the right coronary cusp, which presented with syncope secondary to hypotension thought to be resulting from reduced left atrial filling as a consequence of transient RVOT obstruction. The case demonstrates how echocardiographic and angiographic images correlate and also an unusual mechanism of syncope.