The distinction between heat and work only comes about in statistical physics. The idea is that while work is a transfer of energy through the macroscopic degrees of freedom which are described by macroscopic (i.e. thermodynamic) quantities (like pressure and volume), heat is a transfer of energy through the remaining degrees of freedom which are ignored in the macroscopic description.
In the above sense, the distinction between work and heat is in some way artificial. It is induced by our choice of which degrees of freedom we want to consider in our description of a physical system and which ones we chooses to be ignorant about. This is also means that temperature and entropy are basically dependent on the convention one chooses to describe the system. This perfectly matches the idea from information theory where the amount of information contained in a message is characterized by the so called Shannon entropy which is exactly the same thing as the physical entropy, except for the factor of $k_B$: a message like "The OP's name is 21Brunoh." contains exactly zero information to you because you already knew that. That same message may however be considered quite informative by someone unaware of this thread. Thus, information is a observer-dependent concept. Entropy characterizes the lack of information.
In thermodynamics however, there is a natural ("canonical") choice of the quantities of a physical system one can know about (like pressure, number of particles) and those which are inaccessible (like the positions and momenta of all the individual particles). The latter lead to a lack of information, characterized by the (physical) entropy. Changes in the observable/macroscopic quantities are called different forms of work, i.e. changes in pressure and volume are referred to as mechanical work. Changes in temperature and entropy are referred to as heat.