Is Donaire’s heart still in the fight place?

Guts, sand, grit, chutzpah. Whatever your preferred variant of the concept, we all get what “heart” is supposed to mean — particularly it’s definition when viewed through the prism of prizefighting.

And what of Nonito Donaire Jr., who will face Nicholas Walters tonight in Carson, California. Does he have it, heart? Judge for yourself:

As a professional, Donaire has fought on 35 occasions — valiantly, ferociously in most cases — and has lost just twice. The first defeat came in Donaire’s second bout, at the hands of the not-so-immortal Rosendo Sanchez. Donaire was undeterred.

What followed were 30 consecutive victories, Donaire’s first world title (a name-making 2007 knockout of flyweight brawler Vic Darchinyan), the 2011 KO of the year (a one-punch lambasting of bantamweight titlist Fernando Montiel), the 2012 fighter of the year award and five more recognized belts across three additional divisions.

Whatever you think of today’s titles and championship designations spilling uncontrollably from the various sanctioning organizations, Donaire has done as much as any fighter in recent years to legitimize — in the moment, at the very least — the value of those belts he fought for and held. He beat real fighters, gained their hardware fair and square, never ducking a dangerous challenge before or after.

Donaire is also — and I say this with admiration — the sensitive type. He’s an amateur photographer. He’s a doting family man — the real thing, by all accounts. His wife, Rachel, is an equal partner in his career. Cripes, his son’s name, Jarel, is a sappy-sweet acronym — it stands for “Junior and Rachel’s everlasting love” — that would be brutally difficult to live down around most testosterone-lacquered boxing gyms. A year ago, Nonito Donaire Sr. — Junior’s only trainer before a years-long falling out — returned to the fold after a tearful reconciliation.

For all the world, Nonito Donaire Jr. seems to be all heart.

But recent events — most critical among them last year’s lackluster loss to Cuban southpaw and current junior featherweight kingpin Guillermo Rigondeaux — have prompted a different sort of question: With 13 years in the game come and gone, and at age 31, is Donaire’s heart still, specifically, in boxing?

Just examine his latest results in the ring: A 2011 Madison Square Garden stinker, immediately following the spectacle of the Montiel knockout, against Omar Narvaez. Donaire couldn’t prevent the elusive junior bantamweight champ (who had moved up in weight for the bout) from running. But looking back, might he have at least pressed the issue further? Next came a split-decision win over Wilfredo Vazquez Jr., which wasn’t as close as the decision suggested but was hardly dominant. In fact, Donaire didn’t really look himself again until blasting out the faded Jorge Arce in late 2012.

The revival didn’t last. In his next fight, at Radio City Music Hall last March, the California-based Donaire saw his efforts at conquering New York again fall flat. Rigondeaux, an all-time amateur great making just his 12th professional fight — and who is quite possibly some sort of boxing warlock — made Donaire look slow, lost and almost foolish. Save for one conspicuous lapse, when Rigo went down on a flash knockdown in the 10th round, he owned seemingly every moment of the fight.

A sluggish rematch win over Darchinyan (by then 37 years old) and a technical-decision victory over unknown Simpiwe Vetyeka — in which a Donaire cut stopped the bout short — did little to restore faith in Donaire’s once-unimpeachable force of will.

With Walters on deck, we should learn the answer to any remaining questions about Donaire’s heart, and where it lies, in a matter of hours. A 28-year-old, undefeated Jamaican, Walters most recently blitzed Darchinyan — the latest act in an ongoing tour de force (20 KOs in 24 fights). Darchinyan is on his last legs, and Walters admittedly has faced no other opponents who compare to the top dozen in Donaire’s dossier. But everyone, including Junior, admits that the challenger is a threat. Most sportsbooks are calling it an even-money fight, and some even favor Walters.

With middleweight assassin Gennady Golovkin set to tee up Marco Antonio Rubio in the StubHub Center main event, the real intrigue Saturday night will play out in the undercard — an unfamiliar scenario for Donaire in every sense. We should soon know if “The Filipino Flash” whom fans warmed to over the years still burns inside Donaire, or if the pilot light is out for good.