Strength of the Heart in Chinese / Japanese...

This can be translated as, "with all one's strength," "with all one's heart," "to the limits of your heart," or "to the end of your heart/emotions."

The character breakdown:
思い (omoi) thought; mind; heart; feelings; emotion; sentiment; love; affection; desire; wish; hope; expectation; imagination; experience
切り (kiri) bounds; limits.

Note: Because this selection contains some special Japanese Hiragana characters, it should be written by a Japanese calligrapher.

This title speaks of one's soul or spirit, and the capacity or strength that soul possesses.

The first two characters mean mind, heart, spirit, and/or soul.

The last two characters mean strength, capacity, or ability.

Note: Separately, these are two words in Japanese, and can be pronounced but this does not make a natural title in Japanese (best if your audience is Chinese).

This phrase can mean either "strong hearted," "strong willed" or "determination."

The first two characters can be translated as "will," "willpower," "determination," "volition," "intention," or "intent." But, it should be noted that this first part possess the element of "heart" in the lower portion of both characters (they also partially carry the meaning "with whole heart").

The last two characters mean "strong" or "staunch."

Chinese word order and grammar is a bit different than English, so in this case, they are in reverse order of English but have the correct meaning in a natural form.

See Also:  Strong Willed | Discipline | Will-Power

鉄心石腸 is a Japanese proverb which suggest you should have the inner-strength and will as hard and steadfast as iron. It's the Japanese way to say, "stay strong." 鉄心石腸 is an especially uplifting thing to say to a person in distress or recovering from a disaster. It's kind of the survivor's creed.

If you literally translate this, it means, "iron will, stone guts" or "iron heart, rock-hard bowels."