Final answer:
Heathcliff opening the window symbolizes his wish to be reunited with Catherine and to find freedom and peace in the afterlife.
Step-by-step explanation:
When Heathcliff opens the window on his last night of life in Emily Brontë's "Wuthering Heights", it symbolizes his desire to reunite with his lost love, Catherine. This act represents Heathcliff's longing for freedom from his tormented life and his wish to be with Catherine, even in death. The open window is a conduit to the spiritual world, suggesting Heathcliff's readiness to release his soul and finally find peace.