SQL Server Merge Update Insert Stored PROCEDURE

Here is my Example for single row MERGE / upsert in SQL Server.

This Stored PROCEDURE get input and upsert into the table.

It's faster than do select count(1) before insert/update.

CREATE PROCEDURE [dbo].[PROC_Heartbeat_Save]
	-- Add the parameters for the stored procedure here
	@session_id varchar(50),
	@user_id int,
	@system_id varchar(32)
AS
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;

	-- Saving Session info
    MERGE [dbo].[Heartbeat] AS T
    USING
    (
        SELECT @session_id
           ,@user_id
           ,@system_id
    ) AS S
    (      session_id
           ,user_id
           ,system_id
    )
    ON (T.session_id = S.session_id and T.user_id = S.user_id)

    WHEN MATCHED THEN
        UPDATE SET last_uptime = GETDATE()

    WHEN NOT MATCHED THEN
        INSERT
            ([session_id]
           ,[user_id]
           ,[system_id]
           ,[usb_serial]
           ,[version]
           ,[firmware_slot])
        VALUES
            (@session_id
           ,@user_id
           ,@system_id
           ,@usb_serial
           ,@version
           ,@firmware_slot)
    ;

END