Breathing mixtures containing helium are used for deep dives, because helium is not narcotic and is less dense than nitrogen. In the late 1980's, pioneer technical divers adopted trimix (helium-nitrogen-oxygen) instead of heliox (helium-oxygen) for open-circuit deep diving. Trimix often contained a relatively low fraction of helium and high fraction of nitrogen, because these divers had limited infrastructure to mix helium into high-pressure scuba cylinders and helium is expensive. With adoption of closed-circuit rebreathers, technical divers are beginning to dive with higher fractions of helium, and even heliox. These divers find that some popular decompression algorithms can prescribe a greater amount of decompression for a heliox bounce dive than for a corresponding bounce dive conducted breathing trimix or nitrox. Is this extra decompression really required? To answer that we will review the evidence, from the first heliox dives in the 1930s through to recent experiments.