Patients have hearts over their head that indicate their health. If they lose all hearts, they will leave the hospital and you lose the income. There are upgrades that will slow their health loss. Purchase television sets, plants, water, and food stations to give their hearts better life. When a patient is low on health, as a warning their face will appear in the corner. Either deal with them or refer them to another medical center. You still get some money for the referral, which is better than nothing if they leave.