Volhard made several important contributions in the fields of cardiology and nephrology. He is especially remembered for his collaborative work with pathologistKarl Theodor Fahr (1877–1945) in Mannheim, where the two men carried out research of kidney diseases. The two physicians created a classification system of renal disorders, making the differentiation between degenerative (nephroses), inflammatory (nephritides) and arteriosclerotic (scleroses) diseases.[1] With Fahr, he published a classic monograph on Bright's disease called Die Bright'sche Nierenkrankheit, Klinik, Pathologie und Atlas.
Volhard recognized that constrictive pericarditis was a treatable condition, and as a result of his research with Viktor Schmieden (1874–1945), it led to the first pericardectomy for constrictive pericarditis. Volhard also performed extensive studies involving renovascular hypertension and uremia. Regarding uremia, he divided associated symptoms into two criteria called "true uremia" and "pseudo-uremia". Pseudo-uremia was described as having symptoms of independent origin, such as cases involving elevated arterial blood pressure.
In 1903, Volhard was credited with the discovery of lipase in the heart and kidney. He also developed a method of preserving cardiac specimens via a process of dehydration and the application of hot paraffin. In 1917, he joined the German Fatherland Party. In Berlin the "Franz-Volhard-Klinik" is named in his honor.