The success of LV lead placement varies from 70-90%.1-3 A lower success rate is typical for attempts during the operator s early experience, and even the experienced operator still encounters challenging anatomy. Failed implantation necessitates an additional surgical procedure for epicardial lead placement in 5-10% of cases; worse yet, in centers without an experienced or dedicated surgeon, it may lead to abandonment of CRT for that patient entirely. One of the challenges that may lead to difficult or failed LV placement is CS cannulation, especially when cardiac anatomy is distorted in patients with dilated cardiomyopathy. In these patients, the coronary sinus takes on a different shape and curvature, making cannulation more difficult than in patients with structurally normal hearts. Thus, even an experienced cardiac electrophysiologist with significant experience in coronary sinus cannulation for diagnostic cardiac electrophysiology studies can encounter quite a challenge. Noninvasive imaging of the coronary venous anatomy has shown that the relationship between the coronary sinus and the right atrium in patients with a significant history of congestive heart failure is quite different from that in patients with normal hearts (control subjects).4 In patients with dilated cardiomyopathy, the coronary sinus empties into the right atrium at an angle, resulting from a higher than usual CS ostial entry with downward course of its proximal portion (Figure 1). This distortion of the CS-atrial relationship can create significant hindrance to entering the CS using the standard cannulating sheaths and catheters because of the curvature mismatch (Figure 2). Secondary tools with countercurves have been helpful in entering the CS, but subsequent advancement of the sheath and lead can be a challenge. Furthermore, identification of the CS ostium location may take longer than usual. In reviewing recent data from our institution, it appears that in 60% of cases, the CS os could be found, and the CS cannulated within approximately five minutes. In the remaining 40% of cases, CS cannulation times clustered around 20 minutes; occasional very long cases or cannulation failures are also known to occur. These delays contribute to prolonged total procedure times and, not infrequently, are concomitant with further delays due to lead instability and dislodgement also resulting from anatomical distortion. Even for the experienced implanter, CRT procedures can often take over two hours. For inexperienced implanters, procedure times of 3-4 hours are not unusual. Clearly, such a situation is not only frustrating to the operator and impractical for a busy Cardiac Electrophysiology Laboratory, but it also affects procedural safety and morbidity. In some centers, preoperative non-invasive evaluation is performed to anticipate these difficult cases. Noninvasive imaging is also useful in identifying the presence or absence of a suitable coronary vein tributary, the coronary venous anatomy being much more variable than its arterial counterpart. In a significant minority of cases, the posterior or lateral vein is either absent or not suitable due to its size or tortuosity.3 Thus, patients with non-suitable coronary venous tributaries may be better served by minimally-invasive surgical implantation of an epicardial lead for LV pacing. Other obstacles to CS cannulation include the presence of prominent valves (Figure 3) or fenestrations at the coronary sinus ostium, which are estimated to be present in 1-5% of patients.5,6 These valves and fenestrations are not readily seen during cannulation or even after contrast venography. Of note, coronary venous valves can also be present throughout the course of the vein. Of clinical significance is the Valve of Vieussen, at the transition between the coronary sinus and great cardiac vein (at the site where the vein of Marshall usually empties) (Figure 4). In cases where the Valve of Vieussen is prominent, advancement of a balloon catheter, sheath or LV lead can be hindered or result in coronary vein dissection (Figure 5). One new tool for better identification and navigation of coronary venous anatomy is a direct visualization catheter (Acumen Medical, Inc., Mountain View, California). This catheter enables visualization of various anatomical landmarks in the heart, such as the atrial trabeculation, tricuspid valve and, importantly, the coronary sinus os. Direct visualization can also detect the presence of valves and fenestrations that may obstruct the opening into the coronary sinus (Figure 6) which could not be detected from standard fluoroscopy images (Figure 7) as well as aid in the identification of junctions of the coronary vein tributaries. Equipped with a balloon, this catheter can also serve as an occlusive device for coronary venography. Such direct visualization may facilitate the placement of LV leads for CRT procedures and ultimately reduce the operator s failure and frustration and enhance efficiency in the Cardiac Electrophysiology Laboratory.