Praying for him. Chest pains can be weird, and caused by many possible things. Sometimes what you think is real bad actually is not (e.g., the time I had *really bad* heartburn after eating really spicy food, and my wife thought it was another heart attack), and other times you think it is nothing and it is bad (e.g., I still don't recognize when I had my first heart attack, and my second did not seem like your traditional heart attack).
Let them check him out real good. Usually an plain electrocardiogram shows if there has been a heart incident. Even better, I am glad to hear the nuclear stress test turned out ok -- that detects a lot of heart issues beyond just an electrocardiogram. However, you may not be able to rule out the heart 100% unless they do an angiogram, but the nuclear stress is close to 100% for identifying whether a problem is likely.
If it is not heart, he should be out soon. Like pdlong said, it could be just an imbalance. Potassium levels can affect the heart a lot, and potassium can be affected by fluid levels (e.g., a diuretic depletes potassium). Sometimes something as simple as caffine, or tension, can cause a constriction that can produce some chest pain. Even something as dumb a s muscle pull can feel real bad if it is the wrong muscle.
Let us know what happens.
Ken