Hearts had come back from James Fowler's brilliant opener 10 minutes into the second half when Rudi Skacel and Ryan Stevenson netted.
But on-loan Everton striker Agard volleyed home in the 86th minute as Kilmarnock capitalised on some sustained pressure to secure a 2-2 draw.
The thrilling finale made up for a scrappy and bad-tempered first half and saved Killie caretaker manager Kenny Shiels from a third successive defeat, although he remains without a win in five games.
Former Hearts manager Csaba Laszlo, who has expressed an interest in the Rugby Park post, watched from the main stand as Hearts moved eight points clear of Dundee United, who play at Celtic Park on Sunday.
Source: PA
Source: PA