Patients with atrial fibrillation (AF) are at an increased risk of thromboembolism and stroke primarily from the development of thrombi within the left atrial. Pathological changes in blood constituents and atrial endothelial damage promote the left atrial thrombus formation. It is not known whether factors predisposing to left atrial thrombus formation in AF are disease specific or also evident within the normal heart. The present study examined whether there are differences in, platelet reactivity, endothelial function and inflammation in blood samples obtained from intracardiac and peripheral sites in subjects within structurally normal hearts. Sixteen patients with diagnosed left sided supraventricular tachycardia (SVT) undergoing a routine elective electrophysiological study and ablation were studied. Blood samples were taken simultaneously from the femoral vein, right atrium and left atrium, immediately following transseptal puncture and prior to heparin bolus administration. Between peripheral and atrial sample sites patients with SVT showed no change in platelet reactivity or aggregation (CD62P P=0.91, sCD40L P=0.9), thrombus formation (TAT P=0.55), endothelial function (vWF P= 0.75, ADMA P=0.97 and NO P=0.61), or inflammation (VCAM‐1 p=0.59 and ICAM‐1 p=0.69). SVT patients had lower ADMA and ICAM‐1 levels than AF patients. This study demonstrates for the first time in SVT subjects with structurally normal hearts have consistent haemostatic function between atrial and peripheral sites. These results suggest that the atria of SVT patients do not contain predisposing thrombogenic, endothelial of inflammatory factors that promote/initiate thrombus formation. This article is protected by copyright. All rights reserved.