The role of nitric oxide (NO) in the protection of cardiomyocytes against reoxygenation induced cell damage has been investigated in a cell culture model of isolated cardiomyocytes. A temporary contractile blockade at the onset of reoxygenation was found to protect cardiomyocytes from reoxygenation induced hypercontracture, one of the causes of irreversible cell injury elicited by reoxygenation. NO-donors inhibit the contractile response of electrically paced cardiomyocytes. It was therefore investigated whether NO donors can be used to protect cardiomyocytes against reoxygenation induced hypercontrature. This protective effect was indeed demonstrated. The protection is due to the release of NO and mediated through an activation of soluble guanlylate cyclase. A second cause of irreversible cell injury elicited by reoxygenation is increased osmotic fragility. NO donors protect reoxygenated cardiomyocytes against osmotic fragility. This effect is due to a direct action of NO and can be mimicked by radical scavangers. This indicates that NO can protect isolated cardiomyocytes against free radical injury. In conclusion, studies using isolated cardiomyocytes support the hypothesis that NO protects cardiomyocytes against ischemia/reperfusion injury. Whether or not NO exerts a direct protective effect on cardiomyocytes in a more complex system, like in the whole heart in vivo, remains to be elucidated.