Heartless is a cardio workout whose name is the driest joke on the poster: it's about nothing but your heart. Jack burpees, jumping jacks and shoulder taps - two movements that send your pulse climbing and one that refuses to let your arms opt out. The gothic lettering promises cruelty, and technically delivers it, just in the cardiovascular sense: this workout has no sympathy for a heart that would rather coast.

The circuit runs without rest between exercises, and the pattern is a metronome of spikes. Single jack burpees alternate with blocks of 20 jumping jacks throughout the set - and the ratio is the trick. The burpee is one maximal, whole-body event: floor, plank, stand, jump. The jacks that follow aren't recovery so much as sustained elevation, keeping the heart rate high between spikes so it never gets to descend properly before the next burpee arrives. That oscillation between peak effort and steady effort is textbook cardiovascular conditioning, hidden inside a workout that looks like it's mostly jumping jacks. The 20 shoulder taps at the end drop you into a plank and make the shoulders and core close the set while your pulse is still arguing.

Make each jack burpee a full sequence - chest over the floor in the plank, feet jumping wide on the rise, arms finishing overhead. On jumping jacks, stay light on the balls of your feet with full arm arcs; quality holds even at rep 60. In shoulder taps, set feet slightly wide and keep hips dead still as each hand rises.

Heartless in name, all heart in practice - yours, working overtime.

Make it Harder: Turn every single jack burpee into 3.

Make it Easier: Step the jumping jacks as half jacks and step the burpees out and in.