Healing during a combat:

"Vampire characters may spend blood to heal themselves. To do so, the character must concentrate and do nothing else for one full turn. A character may attempt to heal while performing other
actions, but this requires success on a Stamina + Survival reflexive roll (difficulty 8). Failing this roll means the vampire loses all expended blood points with no effect, while a botch causes the vampire to lose both an additional blood point and an additional health level. Spending blood to raise Physical Attributes or power Disciplines may be done automatically,
without the need for concentration. A character may spend an amount of vitae equal to her per-tum rating, as dictated by her
generation."

So, obviously, attempting to heal counts toward the 'blood per turn limit' which reduces its availability for increasing traits or fueling disciplines, the difficulty is rather high, there is a chance of receiving additional damage and bloodloss on a botch, and an even better chance of spending the blood for nothing.

-Courtesy of Zach, found on page 200 of Vampire the masquerade: revised.

Vampires Non-Combat healing:

It should also be noted that Vampires do NOT heal naturally. Wounds taken remain both on your character as well as in the form of dice penalties until enough blood is obtained and burned to heal the wounds.

No amount of medicine skill or first aid application will ever heal someone who is already dead.