To compare the changes in heart function, induced after sedation with midazolam or dexmedetomidine, using cardiac magnetic resonance imaging (MRI).

This study is a randomized unmasked study, in which participant will be allocated by the envelop method into the dexmedetomidine (DEX) group or into the midazolam (MID) group.

The study will test the hypothesis that the use of dexmedetomidine leads to less negative impact on ventricular function compared to midazolam.

The study will include patients who will meet the inclusion criteria. A previous, yet unpublished, pilot study assured that a number of 15 participants in each arm is sufficient to detect statistical significant results with a statistical power of ≥ 80%. After signing the informed consent, a one-session cardiac MRI will be performed in each fasting participant before and after sedation administration (see arms and intervention). The following parameters will be recorded: end diastolic and end systolic volume, left and right ventricle stroke volume and flow velocity through the mitral valve during early and late diastole. A monitor will record values of mean blood pressure, pulse and blood oxygen saturation in 5-minute intervals.

The acquired data will be transferred to an offline workstation for postprocessing and quantification. In participants we will calculate left ventricular volumes using the well-known Simpson's formula by segmenting of endocardial borders on end-diastolic and end-systolic frames on every slice through the left ventricle.

The quantitative flow measurement will be performed using phase contrast quantification flow mapping.

Statistical analyses will be performed using STATISTICA software (data analysis software system, version 13 TIBCO Software Inc). All values will be presented as average ± standard deviation. Analysis of variance for repeated measures with post hoc Fisher's LSD test will be used for statistical testing of significant differences in each group and between the groups before and after sedation, respectively. Significance level will be accepted at α<0.05.

The participants will be monitored during sedation administration and 6 hours following sedation cessation to avoid complications that could be associated with sedation administration such as hypotension or rhythm disturbances.

Inclusion Criteria:

• Patients who were admitted due to chest pain, in whom acute coronary syndrome, pulmonary embolism and acute aortic syndrome were ruled out
• Age ≥18 and ≤ 65 years
• No contraindication to provide cardiac MRI
• No known allergy to Midazolam or Dexmedetomidine
• Signed informed consent
• No history of heart, hepatic, renal or respiratory failure

Exclusion Criteria:

• Atrial fibrilation
• Claustrophobia
• Heart Failure
• Renal Failure
• Hepatic disease
• Respiratory insufficiency
• Fertility and lactation
• Patients who cannot cooperate or refuse to sign the consent.