How to deal with dual reporting lines in matrix organizations?

Best you can. There is no single answer, as dealing with one manager can be difficult if he/she is a difficult person, let alone two.

Usually, subject of reporting in the two lines are different, one is usually organizational (i.e. company / organizational unit / national company you work for), the other functional (i.e. marketing).

Use your best judgment and report fully on topics covered by each manager, but try to be transparent on all issues to both, as managers sometimes like to know everything.

Juggling with multiple balls is not easy, but tends to teach you a lot.

Matrix is the requirement of the organisations where different products are handled by same structural management infused with different product management.

Vision and Mission of the organisation should be valued, respected and therefore realigned to the different departmental's Vision and Mission to meet the common objectives. As long as SUBJECTIVES and OBJECTIVES are understood clearly, the line and structure management will succeed in the Matrix.

Finally It lies on the behaviourial science of the leadership that makes or mar the Matrix. This is very prominently evident when heirarchy boss takes over Matrix set up.

We should not bring in the so called Reporting Phobia  - " Single employee vs Two bosses" for discussion..

Absolutely agree with Jasmina.  people find it difficult to deal with one "Boss"  and here we are talking of two.  What is important here is that firstly these two managers or "Bosses" should be competent enough to work in a MO setup.  If these guys or even one of them is not competent enough to understand that he is sharing his or her employee with one more person, or allow time and space to that employee, its going to be a disaster.  Secondly there has to be trust on that employee who has the dual lines of reporting and should be given enough resources and freedom to be able to manage their time and tasks.  Management of time is extremely important.