♠ Q 4
♥ K J 8 7 5
♦ A J 8
♣ K J 9
Most experts prefer to open 1NT with a balanced hand that falls in the partnership notrump range, even when it includes a five-card major. Here are some of their reasons:
An opening bid of 1♥ covers a wide range of strength and distribution. It could be anywhere from about 13-21 points, and could be balanced or unbalanced. An opening bid of 1NT describes a narrow range of strength, 15-17 points for example, and a balanced hand – no void, no singleton, and no more than one doubleton. It's unlikely that the partnership will stop too low or get too high after such a descriptive opening bid.
If the above hand is opened 1♥, what does opener rebid after partner responds 1♠? 1NT would show a minimum balanced hand of about 12-14 points; 2NT would show a strong balanced hand of about 18-19 points; a jump to 3♥ would show about 16-18 points, but also at least a six-card heart suit; a rebid of 2♣ or 2♦ would show a second four-card suit. There is no attractive rebid.
Over a 1♥ opening bid, left-hand opponent can get into the auction with a 1♠ overcall. This is no longer possible if the opening bid is 1NT. Left-hand opponent will have to enter the auction at the two level. Since responder has a good picture of opener's hand, responder may be able to double an overcall for penalty more effectively.
By not telling the opponents about the five-card heart suit, it is possible that the opening lead may be a heart from left-hand opponent when holding four or more hearts. Even without that, the opponents may have difficulty determining declarer's distribution until it is too late.
After opening 1NT, this hand is likely to become the declarer whenever the partnership plays in notrump, or in a suit contract – after Stayman or a transfer bid, for example. Keeping the strong hand hidden will usually be advantageous during the play. If you were to open the bidding 1♥, for example, and partner were to respond 1NT, now partner is likely to be the declarer and the strong hand will be face up on the table.
So don't hesitate to open 1NT with a balanced hand that includes a five-card major suit.