As the largest of all the Channel Islands, you would rightfully conclude that Santa Cruz Island has a great deal of excellent dive sites. Most of them are fairly well known as many show up on the charts or in guidebooks. Heart Attack Reef, however, does not. While not a virgin reef, fewer divers and fisherman visit here because of its absence from most published material. Yet I rate this location as one of the best on the backside of this big island.

How it gained its name is easily understandable. Far from shore, boats would cruise by at a high rate of speed. With their fathometer clicking away measuring the depth under the vessel, skippers would think they were safe with the flat sand bottom 50-60 feet below. Suddenly, as if out of nowhere, the bottom shoots up to within 12 feet of the surface giving the boat’s skipper a “heart attack” for fear that their vessel was about to run aground. Of course once intrepid underwater explorers learned of its location, diving activities ensued and this site’s reputation as an excellent reef grew rapidly. Even so, much fewer divers visit here than the nearby colorful and more popular Flame Reef.
The attractiveness of this reef is owed to excellent structure and an almost constant current. A series of sharp steep stair-step ledges make up the structure. Many of these ledges are deeply undercut. There are also multiple mini-walls 20 feet high or more. There are a lot of nooks and crannies and overhangs housing a wide variety of marine life. 
Bright “bushes” of red gorgonian are scattered across the reef. Actually an animal, these colonies of thousands of tiny white polyps filter small of bits of food carried in on the current. The whiteness of the polyps against their red stalks gives the colony an overall pink appearance. 
A variety of nudibranchs provide a splash of color. My favorite is the neon blue chromodorid. These little guys bear yellow racing stripes (if you can imagine a sea slug “racing”). Yellow dorids are common as are hermissenda nudibranchs.
Other invertebrates to look for include tube anemones in the sand and gravel at the base of the reef, brown sea hares, and an unusually large number of big sheepcrabs.
Santa Cruz Island is known as a transition zone between temperate water currents from the southeast mixing with colder seas from the west-northwest. Marine life cross-section matches this blend. Bright orange garibaldi from the south swim along side the copper rockfish, common to the north. Rockfish, as a matter of fact, are abundant. Here you will find a lot of olive, kelp and blue rockfish. Other reef fish include numerous greenlings, black eye gobies, and an occasional treefish, including juveniles, that make for macro camera fun.
Don’t ignore the sand and gravel area surrounding the reef. The reef first tapers off in a series of boulders and smaller ledges before hitting bottom at about 50 feet. Lucky divers will encounter big bat rays and small halibut.
This area does not fall within any of the new Marine Protected Areas but it does not really matter as there is very little here to collect in terms of seafood. You might find a random rock scallop or a lone lobster. There are a lot of fish here but rarely any big enough to shoot.
Kelp navigation is not a problem as there is rarely much here, just a few stalks. Surge can be quite heavy on the shallow portions so steer clear. Water clarity is fair to good and varies by season with the fall being best. Currents keep visibility mostly good but use proper current diving techniques. 
Thankfully, Heart Attack Reef is not named after some sort of tragedy but hopefully its beauty will tug at your heartstrings.
Special thanks to the owner, captain, and crew of the dive charter boat Truth for assistance in creating this article. 
Location: Backside (seaward) side of Santa Cruz Island. GPS N33° 59.055′, W119°36.808′
Access: Boat only. Several dive charters out of Santa Barbara and Ventura visit this site regularly.
Skill level: All. Beginners should be cautious in potentially strong current.
Depths: 12 to 50 feet. 
Precautions: Strong surge in shallows.
Visibility: Fair to good, average 30 feet.
Snorkeling: Poor. 
Photography: Good for macro. Fair wide-angle along ledge.
Hunting: Poor.