Heart failure is an established predictor of primary cardiac events during pregnancy. Adequate heart failure treatment in pregnant women is hampered by important foetotoxicity of several conventional drugs. Hydralazine with or without long-acting nitrates has been proposed as an alternative for ACE inhibitors or angiotensin receptor blockers. There are no published data, however, on the use of hydralazine to treat heart failure during pregnancy. We describe the course and outcome of pregnancy in two patients with heart failure. A 31-year-old woman with dilated cardiomyopathy was not treated with hydralazine during pregnancy and developed worsening heart failure. A 36-year-old woman with ischaemic cardiomyopathy was treated with hydralazine early during pregnancy and remained stable throughout and after pregnancy. We assume that early initiation of hydralazine as an alternative for ACE inhibitors or angiotensin receptor blockers during pregnancy in patients with cardiomyopathy could prevent further left ventricular dilatation and worsening heart failure.