Working under the supervision of Rudolf Brdička [cz] at Bulovka Hospital, and in a rudimentary laboratory in the basement of his parental home, he discovered a polarographic method of measuring fast chemical reactions.

[4] Wiesner's role included ensuring an adequate supply of the antibiotic by extracting and purifying the substance from the test subject's urine following treatment.

In the 1950s, prior to the development of nuclear magnetic resonance spectroscopy, he determined the structure of several diterpene alkaloids including veatchine, atisine, annotinine, delphinine, aconitine, and songorine.

Towards the end of the 1970s Wiesner turned his attention to digitalis derivatives, with the goal of finding cardiac glycosides with safer therapeutic ratios.

In the last decade of his career he succeeded in demonstrating the separation of the inotropic and toxic properties of this group of compounds, elucidated the underlying chemical mechanism, and finally achieved the total synthesis of digitoxin and other cardioactive steroids.