Keep getting the same random values when using a function

I want to make a program that will do some kind of battle logs. You strike with 50% chance of hitting the enemy and deal damage from 10 to 25.

from random import randint

hitChance = randint(0,1)
damage = 10 + randint(0, 15)
HP = 100

def atack():
    global HP

    if hitChance is 0:
        print("Missed")

    elif hitChance is 1:
        HP -= damage
        print(damage, " delt")
        print(HP, " left")

while HP > 0:
    atack()
    print("You defeated the enemy!")

However when i run this code it either stuck in an infinite loop of "missed" or deals the same damage values.