At 20:00 of 7 December 1966, and under extreme weather conditions, with winds blowing at Force 9 on the Beaufort scale, the Heraklion sailed from Souda Bay, Crete for Piraeus, after a two-hour delay, allegedly in order to embark a refrigerator truck that according to most accounts contributed to the sinking. Nowadays, passenger ships operating in Greek waters are prohibited from sailing in winds at or greater than Force 9 on the Beaufort scale, but at that time it was up to the captain to decide whether to sail or not, sometimes under pressure from the ship owners.
Halfway through the voyage, while sailing south of the small rocky island of Falkonera, the aforementioned refrigerator truck which was carrying oranges and was either left unsecured or was loosely strapped, started banging on the midship loading door which eventually gave in and opened with the result that the truck plummeted into the sea where it was found floating the next morning. With the doors opened, the sea flowed in and after 15 or 20 minutes the ship capsized, sometime after 02:00 on 8 December 1966, at 36°52′N 24°8′E.
At 02:06, an SOS signal from Heraklion was received by various shore stations and ships around the Aegean Sea.
Officially, out of 73 officers and crew and 191 passengers, only 46 were rescued (16 crew and 30 passengers), while 217 died. The exact number remains unknown since, at the time, it was customary to board the ship without a ticket, which would be issued upon sailing.