How is synchronous and asynchronous interaction represented on a sequence diagram?

In a sequence diagram, synchronous interaction is represented by a solid arrow with a filled arrowhead pointing from the calling object to the called object. This indicates that the calling object waits for the call to complete before continuing.

Asynchronous interaction is shown with an arrow with an open (empty) arrowhead. This indicates that the calling object does not wait for a response and continues its work immediately after sending the message.

Example:

Object A          Object B
   |                  |
   | ---▶ (synchronous call) ---▶ |
   |                  |
   | ---▷ (asynchronous call) ---> |