Peroxisome proliferator-activated receptors (PPARs) alpha and gamma regulate nearly every step in cellular fatty acid uptake, utilization, oxidation, and storage pathways. They also control cell growth and migration, oxidative stress, and inflammation in the cardiovascular system. Recent studies have shown that PPARs have paradoxical effects on cardiovascular diseases, especially hypertension and heart failure. It is still unclear whether the blood pressure increases or decreases after treatment with a PPAR alpha agonist; it is also uncertain whether PPAR agonists are beneficial or harmful for heart failure. In order to clarify these issues, the literature on PPAR alpha and gamma and their agonists, as well as their effect on hypertension and heart failure not only in humans but also in experimental animals, was reviewed.