Studies have shown that the calcium ion (Ca(2+)) plays important roles both in Alzheimer's dementia and SARS-CoV S-mediated fusion to host cell entry. An elevated level of intracellular calcium causes neuronal dysfunction, cell death, and apoptosis. Dysregulation of calcium has also been shown to increase the production of amyloid beta (Abeta) protein, the hallmark of Alzheimer's dementia. Reversely, deposition of Abeta is also responsible for calcium dysregulation. On the other hand, it has been well investigated that viruses can disturb host cell Ca(2+) homeostasis as well as modulate signal transduction mechanisms. Viruses can also hijack the host cell calcium channels and pumps to release more intracellular Ca(2+) to utilize for their life cycle. Even though evidence has not been reported on SARS-CoV-2 concerning Ca(2+) regulation, however, it has been well established that Ca(2+) is essential for viral entry, viral gene replication, and virion maturation and release. Recent reports suggest that SARS-CoV needs two Ca(2+) ions to fuse with the host cell at the entry step. Furthermore, some calcium channel blockers (CCBs), such as nimodipine, memantine, etc., have been reported to be effective in the treatment of dementia in Alzheimer's disease (AD) as well as have shown inhibition in various virus infections.