To find the theoretical probability of picking a heart from a standard deck of 52 cards, we can use the formula for probability:
\[ P(\text{event}) = \frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}} \]
In this case, the number of favorable outcomes (the hearts) is 13, since there are 13 cards in the hearts suit. The total number of outcomes is 52, the total number of cards in the deck.
So, the probability \( P(\text{heart}) \) is:
\[ P(\text{heart}) = \frac{13}{52} \]
Now, we can simplify this fraction:
\[ \frac{13}{52} = \frac{1}{4} \]
Thus, the theoretical probability of picking a heart from the deck is:
\[ \boxed{\frac{1}{4}} \]