Lift the heart by its apex to expose the four pulmonary veins, which enter the left atrium [cross-section]. Cut the veins as close as possible to the pericardial sac to avoid damaging the posterior wall of the left atrium.
Cut the serous pericardium that separates the oblique pericardial sinus from the transverse pericardial sinus and remove the heart .
Links and References:
Rohen/Yokochi: 251, 254