Mackenzie Kirk’s second-half penalty was saved before Killmarnock keeper Aiden Glavin produced top stop to deny Michael Aitken an equaliser in injury time.
A Hearts error on 39 minutes allowed Aaron Brown to score what proved to be the only goal for Kilmarnock.
“I think frustration is the feeling more than anything,” Naysmith told the Hearts website. “We miss a penalty, and their 'keeper makes an unbelievable save. I'd say we probably just shaded it in terms of chances.
Most Popular
-
1
Hearts to sign new forward with Stephen Kingsley set to return
-
2
Predicted Hibs starting XI for Livingston clash - with post-derby decisions to make for Hibs boss
-
3
Hearts' European opponents confirmed as former Tynecastle winger prepares to return
-
4
Predicted Hearts XI for visit of Dundee United - with huge clash against Zurich in manager's mind
-
5
Zurich v Hearts live on TV as Europa League play-off tie is beamed back to Scotland
“The pleasing thing is that they're trying to do what we're asking them. They're not trying to shy away from it and they're understanding that they're good players.
"Those are the good things I'm seeing from them and although I'm disappointed with the result, we controlled a lot of the game.
“It was an individual error that cost us, but overall, I can't ask for anymore from the boys. They tried, they played under pressure and were comfortable with taking the ball under said pressure.”
Naismith has been trying to tap into his experience as a young player coming through the ranks to help his team learn to cope with mistakes, demands and expectations.
He aded: “The demands we're placing on them are big, but they need to be able to handle those demands if they're going to make it in the professional game. That starts from Under-18s upwards.”