What effects does operating in an open economy add to expansionary monetary policy? To contractionary monetary policy?

Expansionary monetary policy would decrease interest rates in the U.S. That would reduce real interest in the U.S. relative to other countries, which would make investing in the U.S. relatively less attractive relative to other countries. That would reduce the demand for dollars, lowering the exchange rate value of the dollar, which would lead to an increase in net exports (as well as domestic investment) and aggregate demand. Contractionary monetary policy would have the opposite effects.