The Medic

The Medic is a Teutonic man of medicine. While he may have a tenuous adherence to medical ethics, he is nonetheless the primary healing class of the team. Although the Medic's Syringe Gun and Bonesaw aren't the greatest weapons for direct combat, he can typically still be found near the front lines, healing wounded teammates while trying to stay out of trouble.
When the Medic focuses his Medi Gun on a teammate, they will regain health points. Teammates who are already at full health will have their health buffed beyond the normal limit, up to 150% of their base health capacity. Teammates who have not taken damage recently will be healed more rapidly, encouraging smart withdrawals when injured.
When healing, the Medic will gradually fill a unique ÜberCharge bar, which can fill faster if healing injured or non-overhealed teammates. When the ÜberCharge bar is fully charged, the Medic's healing gun will begin to crackle with small jolts of electricity around it, indicating that he can now deploy a unique charge to benefit his patient and himself for eight seconds. A charge from the Medi Gun offers temporary invulnerability, from the Kritzkrieg: guaranteed critical hits for his patients, from the Quick-Fix: rapid healing and immunity to knock back, and from the Vaccinator: enhanced damage resistance.
Although the Medic cannot heal himself, unless by means of an ÜberCharge-deployed Quick-Fix, he is capable of slowly regenerating health over time, and is the only class capable of doing so naturally. The longer a Medic stays out of combat and avoids taking damage, the greater the increments of health which he will passively heal. An injured Medic will begin regenerating health at a rate of 3 health points per second, scaling up over the following ten seconds to a maximum of 6 health per second (This base rate can be positively affected by the Amputator and negatively affected by the Blutsauger).