  Context: One of the most prominent processes suggested to heat the corona to
well above 10^6 K builds on nanoflares, short bursts of energy dissipation.
  Aims: We compare observations to model predictions to test the validity of
the nanoflare process.
  Methods: Using extreme UV data from AIA/SDO and HMI/SDO line-of-sight
magnetograms we study the spatial and temporal evolution of a set of loops in
active region AR 11850.
  Results: We find a transient brightening of loops in emission from Fe xviii
forming at about 7.2 MK while at the same time these loops dim in emission from
lower temperatures. This points to a fast heating of the loop that goes along
with evaporation of material that we observe as apparent upward motions in the
image sequence. After this initial phases lasting for some 10 min, the loops
brighten in a sequence of AIA channels showing cooler and cooler plasma,
indicating the cooling of the loops over a time scale of about one hour. A
comparison to the predictions from a 1D loop model shows that this observation
supports the nanoflare process in (almost) all aspects. In addition, our
observations show that the loops get broader while getting brighter, which
cannot be understood in a 1D model.
