A heart is randomly chosen 7 out of 12 times from the cards shown. Find the experimental probability of choosing a heart.
The experimental probability of choosing a heart is:
$$
\frac{\text{number of times a heart was chosen}}{\text{total number of times a card was chosen}} = \frac{7}{12}
$$
Therefore, the experimental probability of choosing a heart is $\boxed{\frac{7}{12}}$.