The heart

{3}, {t}: left side of the heart (put an oxygen
counter on target permanent an opponent
controls and target permanent you control)
{2}, {t}: right side of the heart (put a deoxygenate counter on any target)
{1}{w}, {t}: pulmonary vein (if you control the left
lung and the right lung send any card with an
oxygen counter on it and without a deoxygenate counter on it to the graveyard)