We report a preterm infant with 30 weeks of gestation, that received broad spectrum antimicrobials during the first days of life. At nine days of life, the infant appeared with abdominal distension and hematochezia. A systolic murmur with changing auscultatory features also appeared. An echocardiography showed an atrial vegetation. A yeast, that was identified as the emergent pathogen Saccharomyces cerevisiae appeared in two blood cultures. Treatment with amphotericin B was started, the dose was adjusted calculating the minimal inhibitory concentration of amphotericin B, and measuring plasma levels of the antimicrobial. Therefore the minimal effective dose was prescribed, avoiding its deleterious effects. After 14 days of antifungal therapy, a new echocardiography showed a reduction in the size of the atrial vegetation. At 35 days, it disappeared and amphotericin B was discontinued. On the outpatient follow up, the infant has shown a normal growth and a normal cardiac auscultation.