var lastScrollY = 0; //滚动条距顶部位置
function heartBeat() {
    var diffY;
    if (window.document.documentElement && window.document.documentElement.scrollTop)
        diffY = document.documentElement.scrollTop;
    else if (window.document.documentElement)
        diffY = window.document.documentElement.scrollTop
    else
    { /*Netscape stuff*/ }

    percent = .1 * (diffY - lastScrollY);
    if (percent > 0) percent = Math.ceil(percent);
    else percent = Math.floor(percent);
    try {
        window.document.getElementById("gvLeftAd").style.top = parseInt(window.document.getElementById("gvLeftAd").style.top) + percent + "px";
    } catch (ex) { }
    try {
        window.document.getElementById("gvRightAd").style.top = parseInt(document.getElementById("gvRightAd").style.top) + percent + "px";
    } catch (ex) {

    }
    lastScrollY = lastScrollY + percent;
}

window.setInterval("heartBeat()", 100); //每0.1秒钟执行一次