Fluid balance is essential for life. Some studies have shown an association between high intake of water and a low risk of cardiovascular diseases. However, the evidence is insufficient or inconsistent to draw substantial conclusions. The author's objective was to review previous studies addressing the influence of drinking water and hydration status on the cardiovascular system. The PubMed and Google Scholar databases were searched using relevant terms. Animal and human studies in the English language which were highly relevant to the topic were selected and summarized. Drinking about half a liter of water rapidly raises sympathetic activity as much as classic sympathetic stimuli such as caffeine and increases plasma norepinephrine leading to peripheral vasoconstriction. However, cardiac vagal tone enhancement with water ingestion buffers the pressor effects of sympathetic activation. Dehydration leads to mild hypernatremia which gradually causes changes such as increased blood viscosity, hemoconcentration, inflammatory signals, platelet activation and aggregation, adhesive properties of endothelial cells, thrombogenesis, and so on, all of which are harmful to the cardiovascular system. Overhydration can result in water intoxication and increase coagulability. Both dehydration and overhydration are associated with several adverse effects on the cardiovascular system. However, the data regarding how much water can reduce the risk of heart disease is limited and the results are also controversial. More research is needed to confirm the observed associations between hydration status and cardiovascular diseases. Manuscript profile