Stuart McCall's side triumphed 1-0 at Tynecastle thanks to a solitary first-half goal from former Hearts striker John Sutton, and they have now taken 18 points from a possible 18 since losing 5-0 at home to Celtic just over a month ago.
Motherwell are third, a point behind second-placed Aberdeen but with a game in hand. The Dons won 1-0 at home to Hibernian on Friday thanks to Willo Flood's late goal, their fourth straight win ending Hibs' recent revival.
However, Derek McInnes's side remain ten points behind Celtic at the summit, and the reigning champions have two games in hand.
They are not in action this weekend, having opted to take a winter break and participate in a friendly competition in Turkey instead.
At the foot of the table, Hearts are now 20 points adrift of Ross County, who came from 3-1 down to draw 3-3 with Partick Thistle at Firhill in a game which featured braces from Lyle Taylor for the Jags and the Slovak Filip Kiss for the visitors.
In-form Stevie May was on target as St Johnstone beat St Mirren 2-0, while fourth-placed Dundee United go to Inverness Caledonian Thistle, in fifth, on Sunday.