Merge two Lists of different types

I add data to the objects of a List from another List:

public void MergeLsts(List<A> lstA, List<B> lstB)
{
    foreach (A dataA in lstA)
    {
        foreach (B dataB in lstB)
        {
            if (dataA.ItemNo == dataB.ItemNo)
            {
                //dataA.ItemDescription is up to this point empty!
                dataA.ItemDescription = dataB.ItemDescription;
            }
        }
    }
    DoSomethingWithTheNewLst(lstA);
}

This works perfectly fine. However it takes pretty long because both lists get quite large (around 70k items in lstA and 20k items in lstB).

I was wondering if there is a faster or more efficient way to accomplish what I need? Maybe with LINQ?