Influence of Tocolytical Medications on Hemodynamics (Central and Peripheral) and Vascular Function in a Pilot Study to Determine the Design of the Final Study and the Final Study Itself

Inclusion Criteria: * Age between 20 and 40 years old; * In good health, especially no cardiovascular diseases, obstructive lung diseases, chronic kidney diseases or diabetes mellitus. * Using a proper anticonception method (orally, subcutaneously); * A negative pregnancy test. Exclusion Criteria: * Intolerance of Ritodrine; * On chronic medication, except oral and subcutaneous contraception * History or present presentation of cardiac arrythmias; * Risk of being pregnant or less than 6 months postpartum; * Giving breastfeeding; * Previous uteral surgery; * Using an intra-uteral device (IUD); * A severe addiction: nicotine (\> 10 cigarettes/day), alcohol (\> 3 units/day), caffeine (\> 5 units/day) or any extralegally drugs.