Single room MVHR systems are of two types.
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Those with one opening have a heat absorbing element. They take room air and expel it through the element. Then after a short interval the air direction changes and outside air is directed through the same element, absorbing heat as it goes. The cycle then starts at the beginning again.
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Those with two openings to the outside world work just like a whole house system except that there are no ducts to other rooms. By that I mean that they simultaneously take in fresh air from one opening and expel stale air from the other. There is a conventional heat exchanger between the two air flows. The incoming air is directed away from the unit, optionally with a short length of narrow ducting (narrow as it only needs to carry one room’s worth of air). If using ducting you could potentially direct the fresh air to an adjacent room, thus ventilating 2 rooms.