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Guide catheters smaller than 6 Fr can be advanced over the guidewire and balloon catheter shaft to sub‐selectively engage the proximal or mid segment of an artery (Figure 5.5). This technique is also referred to as active engagement or “deep seating” of the guide catheter. The risk of damage to the artery can be minimized by ensuring that the catheter is advanced coaxially over a balloon already inside the vessel. Stabilization of the system while advancing the guide catheter is sometimes required and can be achieved by inflating a balloon within the artery. When considering the use of active support, it is important to bear in mind that deep engagement of large arteries can cause profound ischemia. The use of side holes may not prevent and may even delay detection of catheter‐induced ischemia. A further risk is that of air embolism following aspiration through the Y‐connector while the back pressure in the guide catheter is reduced as a result of damping inside the artery. Despite these risks, for a skilled operator capable of rapidly advancing and withdrawing catheters, active support offers an efficient solution in most cases.