To the Editor,We thank the authors for their interest and comments regarding our paper entitled “Left atrial spontaneous echo contrast and thrombus formation at septal puncture during percutaneous mitral valve repair with the MitraClip system of severe mitral regurgitation: a report of two cases” published in Anatol J Cardiol 2014; 14: 549-50 (1).It is common preference to initiate administration of heparin after transseptal access has been safely performed because of the possibility of occurrence of bleeding complications. We also administered unfractioned heparin after transseptal puncture in both our cases. However, this short dwell time of catheters within the left atrium without heparinization may be sufficient for thrombus or spontaneous echo contrast (SEC) formation within the left atrium. Ideally, heparin should be administered following venous and arterial sheath placement but before transseptal puncture. In our recent cases, as we have gained extensive experience with transseptal catheterization, we have started early administration of low-dose heparin (2000-2500 U) before transseptal access to minimize the risk of thrombus formation and embolism.In both the current cases, another mechanism of thrombus and SEC formation within left atrium after MitraClip implantation could be the disappearance of protective effect of severe mitral regurgitation against the generation of left atrial thrombus and SEC and the reduced mitral valve area due to MitraClip. Immediately after publication of our article, another case report supporting our hypothesis was published by Ohno et al. (2). In their article, the authors described a patient in whom acute SEC appeared in the left atrium after complete reduction of MR with two MitraClips. When the second clip was withdrawn, SEC immediately disappeared in their case. This finding confirms “wash out” effect of regurgitant blood even in acute period.