You chose to lead the 4 of Hearts, the 4th highest of your longest suit. This is the best lead of those given.
Now consider a different hand, and a different set of circumstances. This time the contract is 5 Spades, with both the declarer and dummy bidding in Spades, and your partner bid in Hearts.
Here is your hand.
58. Which card should you lead?
a. 9 of Spades (singleton)
b. 4 of Hearts (lowest in suit bid by partner)
c. 5 of Diamonds (4th highest of longest suit)