Sprinter Sacre heads 26 entries for the Queen Mother Champion Chase at the Cheltenham Festival on 12 March.
Last year's Ryanair Chase winner Cue Card, who may contest the Gold Cup, was among notable absentees.
Sprinter Sacre, now aged eight, won
last year's race
by 19 lengths from Sizing Europe.
The Nicky Henderson-trained horse, previously unbeaten in 10 races over fences,
pulled up in the Desert Orchid Chase
at Kempton last month.
He had an irregular heartbeat which
has since stabilised
came through a gallop
Despite recent events, Sprinter Sacre, who is the highest-rated horse in jump racing since the 1960s, remains favourite to defend the title.
Henderson has also entered Captain Conan, Kid Cassidy and French Opera.
Sire De Grugy, a leading two-mile chaser with three wins from four starts, is entered along with Sizing Europe, who won the 2011 event.
Paul Nicholls' top-class novices Dodging Bullets and Hinterland are potential contenders alongside Al Ferof, who was third in the King George, and has the Ryanair and Gold Cup as potential targets.