Heart Pirates

The Heart Pirates are an infamous and notable rookie pirate crew introduced on Sabaody Archipelago around the time the Straw Hat Pirates arrived there two years ago. Their potential is further seen with the release of Haki by Silvers Rayleigh, against which nearly every notable crewmate was able to withstand.

Past
Trafalgar Law founded the Heart Pirates in North Blue. They fought their way through the Grand Line and eventually reached Sabaody Archipelago.

At some point, Law, the captain of the Heart Pirates was a crew member under Donquixote Doflamingo, where he also met Vergo.

Sabaody Archipelago Arc
On their first appearance, the Heart Pirates were watching a battle between Urouge and Killer, until it was interrupted up by X Drake.

Afterwards they went to a slave auction. While not particularly taking part in the auctions, they watched the events and eventually witnessed Monkey D. Luffy punch Saint Charloss. After the ensuing battle, Rayleigh appeared and used his Haki on everyone, including the Heart Pirates. Every member took it without a problem, except for Shachi, who got a bit dizzy. After the marines started to surround the building, Kid, Luffy and Law went out to deal with them. Eventually Bepo joined the fray as well and Jean Bart was freed from his explosive collar and recruited, choosing his old pirate life over a life as slave. While retreating and trying to escape from the marines, Jean smashed a bridge, to cut the marines off. Shortly afterwards, the crew encountered the Kid Pirates who were in a battle with a Pacifista, though they mistook it for Bartholomew Kuma. Law decided to help the Kid Pirates, in spite of Kid's protest. They fought the Pacifista together. While the battle was not shown, the Heart Pirates were shown to escape without any lasting damage.

Marineford Arc
During the Whitebeard War, the crew was still present on the on Sabaody Archipelago. They were just about to leave.

Later on, the crew appears on the battlefield to save Luffy. Due to Buggy distrusting the Heart Pirates, he did not hand a badly wounded Luffy and Jinbe over right away. However, both the crew and Buggy started to panic when Kizaru attacked Luffy, Jinbe and Buggy, so Buggy handed them over to the crew despite his mistrust. The crew then submerged with their submarine and managed to escape all three of the Admirals' attacks.

Post-War Arc
On their journey, a marine battleship came along with them. It was shown that Boa Hancock, Iva and his okamas were on the Marine battleship, much to the pirate crew's relief. Boa Hancock then invited the Heart Pirates to treat Luffy on Amazon Lily.

After Luffy's treatment was over, the Heart Pirates headed off, though unlike many other pirates, Law decided to stay in "Paradise" for a bit longer.

Punk Hazard Arc
The Heart Pirates were not present on Punk Hazard, aside from Law. However he forms an alliance with the Straw Hat Pirates on behalf of all his crew. It was revealed that they are waiting on another island called Zo to meet up with Law, after his plan succeeds.

Jolly Roger
Unlike many other pirates from the North Blue, the Heart Pirates do not use a skull and crossbones, but a smiley instead. The Heart Pirates' has protrusions in six directions, and is in fact pretty similar to that of the Donquixote Pirates, without the cancel sign over it.

Crew Members
At least five crew members, including Bepo and the newly recruited Jean Bart have been confirmed. Later on, more crewmates were revealed, as seen in Chapter 591. It appears that Bepo, Shachi and Penguin are all proficient in martial arts, in which they all seem stylistically similar. Their captain is also the doctor onboard.

The crew appears to have at least nine members, including Law himself. The most prominent feature of the crew is that they all wear the same boiler-suit apparel, other than Law himself, as well as Bart, a new recruit who changed into a black shirt. A similar clothing design has also been seen being worn by the World Nobles' slaves, with the only notable difference being that the Heart Pirates have their jolly roger on their suits.

Crew Strength
It can be presumed that they are a strong crew for them to have made it all the way to Sabaody Archipelago, and have a captain with such a high bounty.

With the addition of the new member, famous pirate captain Jean Bart, the crew may have grown even stronger. All crewmembers were able to withstand a blast of Haki from Silvers Rayleigh, though Shachi stated that he almost passed out, which may indicate he is slightly less powerful.

Like the rest of Supernovas, they were able to escape Kizaru's raid. They were also able to make it to Marineford, where the war was taking place not long after leaving Sabaody Archipelago.

They also seem to have medical expertise, as their submarine is supplied with what looks like a complete operating theater, and their captain is a medic capable enough to heal Luffy and Jinbe while the former was on the verge of death and the latter was severely wounded.

Given that their captain is a member of the Shichibukai, it is likely that the crew's reputation and strength have increased as well.

Ship
The Heart Pirates use a submarine (潜水艦) as their main mode of transportation.

The vessel seems to display considerable speed and maneuverability when submerged, as seen when it completely outpaced Aokiji's Ice Age, and evaded Kizaru's Yasakani no Magatama. It also seems that the submarine can go through the Calm Belt since it left Amazon Lily without needing to be accompanied by the Kuja Pirates' ship.

Despite the fact that it works like a submarine, its design is similar to a ship as it has a mast and lamps on the outside. Also, on the side of it is the Jolly Roger of the Heart Pirates with the word DEATH (referring to the tattoos on Trafalgar Law's hands and his epithet, "The Surgeon of Death").

From the inside, the submarine seems to be well-equipped with medical apparatuses and life-support systems all stored in the sick bay.

Trivia

 * In the Japanese fandom, Penguin and Shachi were often called "Penguin" (ペンギン) and "Casquette" (キャスケット). The former after the word on his cap, and the latter after the Japanese name of the type of hat he wears.
 * The Heart Pirates' Jolly Roger resembles a virus, a suitable choice considering Trafalgar Law's profession and his epithet: "Surgeon of Death".
 * Also their jolly roger is a "smiley", as first seen used by Law's former superior Donquixote Doflamingo. But unlike Doflamingo's smiley, theirs does not have a "cancel" sign across it. While the significance of the smiley is still unknown, this means whatever it represents, the Heart Pirates support it.
 * All the crew members except for Law, Bepo, and Jean Bart have their face obscured by some kind of hat.
 * Law having a submarine as ship, might be a reference to the Trafalgar class of submarines.
 * Trafalgar Law sailing in a Yellow Submarine could be a reference to The Beatles song Yellow Submarine.
 * The name "Heart Pirates" is likely a reference to Doflamingo's promise to give the "heart" position in his organization to Law
 * The crew may also have been named in honor of Corazon, who was Doflamingo's younger brother.