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Figure 1 Cartoon depicting the occluder component of the second, third and fourth generation buttoned device. The occluder (Occ) in all devices is composed of an x-shaped wire skeleton covered with 1/16-inch polyurethane foam. In the second generation device (left) a 2 mm string loop is attached to the center of the occluder. The loop is closed with a knot (button) made radiopaque. This radiopaque button (ROB) can easily be visualized by fluoroscopy. In the first generation device (not shown), the button was not radiopaque. A folded 0.008-inch nylon thread (NT) passes through the hollow loading wire (LW) after passing through the loop in the center of the occluder. In the third generation device (middle) an extra loop is added immediately beneath the radiopaque button. This modification converted the eccentric button of the second generation device to be aligned straight, thus making it easier to button the Occ and counter-occluder across the atrial septum. In the fourth generation device (right), the button loop is replaced with two "spring" radiopaque buttons (RB), mounted 4 mm apart. The intent was to reduce unbuttoning seen with earlier generation devices.