Merriam-Webster Collegiate Dictionary - importantly

 adverb  Date: 1611  1. in an important way contributed ~ to the language of the field — Ernst Mayr cleared his throat ~ and waited — E. K. Gann the real story is ~ different — Alexander Woollcott  2. it is important that more ~ he stands a chance of having his publication barred — H. L. Mencken Usage:  A number of commentators have objected to ~ as a sentence modifier (sense 2) and have recommended important instead. Actually both the adverb and the adjective are in reputable standard use in this function. Important is always used with more or most had bronze weapons and composite bows; more important, they utilized the horse and war chariot — Harry A. Gailey, Jr. second and most important, the book contains no important woman character — F. Scott Fitzgerald. Importantly is somewhat more flexible in not requiring more or most sticks and, just as ~, unsticks easily — Phoebe Hawkins ~, the leaven in the mixture is quality — George O'Brien.