US President Donald Trump imposed a highest 50% tariff on goods from Lesotho, a tiny African kingdom.
Like the rest of Australia, the Heard and McDonald Islands, the Cocos (Keeling) Islands and Christmas Island are now subject to a tariff of 10%.
A tariff of 29% was imposed on the Norfolk Island, which is also an Australian territory and has a population of about 2,200 people.
The Heard Island, though, is a barren, icy and completely uninhabited - home to Australia's largest and the only active volcano, Big Ben, and mostly covered by glaciers.
The islands are listed by the UNESCO World Heritage as a rare example of an ecosystem untouched by external plants, animals or human impact.